Sensors for three-dimensional printing systems and methods

ABSTRACT

The present disclosure provides methods and systems for printing a three-dimensional (3D) object. The methods may comprise providing, adjacent to a build surface, a film comprising a polymeric precursor. A sensor may be used to determine a profile of the film. The profile may be indicative of a quality of the film. If the profile meets a quality threshold, at least a portion of the film may be exposed to light to initiate formation of a polymeric material from the polymeric precursor, thereby printing at least a portion of the 3D object.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.17/355,394, filed Jun. 23, 2021, which is a continuation ofInternational Application No. PCT/US19/68413, filed Dec. 23, 2019, whichclaims the benefit of U.S. Patent Application No. 62/785,104, filed Dec.26, 2018, which is entirely incorporated herein by reference.

BACKGROUND

Additive manufacturing techniques, such as three-dimensional (3D)printing, are rapidly being adopted as useful techniques for a number ofdifferent applications, including rapid prototyping and fabrication ofspecialty components. Examples of 3D printing include powder-basedprinting, fused deposition modeling (FDM), and stereolithography (SLA).

Photopolymer-based 3D printing technology (e.g., stereolithography) mayproduce a 3D structure in a layer-by-layer fashion by using light toselectively cure polymeric precursors into a polymeric material within aphotoactive resin. Photopolymer-based 3D printers that use bottom upillumination may project light upwards through an optically transparentwindow of a vat containing photoactive resin to cure at least a portionof the resin. Such printers may build a 3D structure by forming onelayer at a time, where a subsequent layer adheres to the previous layer.

SUMMARY

The present disclosure provides technologies relating tothree-dimensional (3D) printing (e.g., stereolithography). 3D printingmethods of the present disclosure may use at least one sensor todetermine a profile and/or quality of a film (e.g., a film of apolymerizable liquid or resin) adjacent to a build surface. If suchprofile and/or quality meet a threshold, 3D printing may be initiated.The present disclosure also provides hardware configurations of one ormore sensors for determining the profile and/or quality of the filmprior to, during, and/or subsequent to exposing the film to light tocontrol a photopolymerization process within the film, thereby printinga 3D structure.

Methods and systems of the present disclosure may provide variousbenefits and advantages. For example, quality control of a 3D printingprocess can be improved by evaluating a quality of a film of apolymerizable material (e.g., resin) adjacent to a build surface, and ifnecessary, re-print the film of the polymerizable material. In somecases, one or more parameters of the film deposition process may bemodified prior to re-printing the film to improve the quality of thefilm to be deposited on a print window. In some cases, quality controlof a printed portion of the 3D object can be achieved by evaluating apattern of any excess polymerizable material remaining on the printwindow. Such pattern or a collection of such pattern may be useful as anegative image (e.g., a silhouette image) of the printed portion of the3D object to assess whether or not the portion of the 3D object wasprinted in accordance to a computer model of the 3D object.

An aspect of the present disclosure provides a method for printing athree-dimensional (3D) object, comprising: (a) providing, adjacent to abuild surface, a film comprising a polymeric precursor; (b) using asensor to determine a profile of said film, which profile is indicativeof a quality of said film; (c) determining if said profile meets aquality threshold; and (d) subsequent to (c), (1) if said profile meetsa quality threshold, using a light source to expose at least a portionof said film to light to initiate formation of a polymeric material fromsaid polymeric precursor, thereby printing at least a portion of said 3Dobject, or (2) if said profile does not meet said quality threshold,adjusting or redepositing said film.

In some embodiments, the method further comprises, in (b), (i) exposingthe film to an additional light and (ii) using the sensor to detect atleast a portion of the additional light that is transmitted through thefilm. In some embodiments, the light has a first wavelength and theadditional light has a second wavelength, wherein the second wavelengthis different than the first wavelength. In some embodiments, the lightand the additional light are provided by a light source. In someembodiments, the light is provided by a light source and the additionallight is provided by an additional light source.

In some embodiments, the method further comprises using an opticaldiffuser, located adjacent to the build surface and away from the film,to diffuse the additional light.

In some embodiments, the method further comprises, prior to (c), usingthe profile to identify a variation in the film with respect to areference. In some embodiments, the quality threshold is a threshold ofthe variation in the film with respect to the reference. In someembodiments, the profile meets the quality threshold if the variation isbelow a threshold variation.

In some embodiments, the profile is an optical profile. In someembodiments, the optical profile is a transmittance profile. In someembodiments, the profile is a two-dimensional (2D) profile. In someembodiments, the method further comprises using the profile to determinea cross-sectional dimension of the film. In some embodiments, theprofile is a thickness profile of the film.

In some embodiments, the film further comprises a plurality ofparticles, and the profile is a density profile of the plurality ofparticles in the film.

In some embodiments, the polymeric precursor encapsulates the pluralityof particles. In some embodiments, the polymeric material encapsulatesthe plurality of particles. In some embodiments, the plurality ofparticles comprises at least one metal particle, at least one ceramicparticle, or a combination thereof.

In some embodiments, (d)(1) is performed with a build head in contactwith the film, and wherein, subsequent (d)(1), the build head is movedaway from the build surface.

In some embodiments, subsequent to (d)(1), the method further comprisesusing the sensor to measure an additional profile of the film adjacentto the build surface. In some embodiments, the additional profile is anegative profile of the at least the portion of the 3D object. In someembodiments, the method further comprises providing an additional filmadjacent to the build surface and using the sensor to determine aprofile of the additional film, which profile is indicative of a qualityof the additional film.

In some embodiments, the method further comprises, in (a), providing adeposition head adjacent to the build surface and moving the depositionhead across the build surface to deposit the film adjacent to the buildsurface.

In some embodiments, the build surface comprises a print window, and thefilm comprising the polymeric precursor is provided adjacent to theprint window. In some embodiments, in (d)(1), the light is directedthrough the print window to the film to initiate formation of thepolymeric material from the polymeric precursor. In some embodiments,the film further comprises (i) a photoinitiator that initiates formationof the polymeric material from the polymeric precursor away from theprint window, and (ii) a photoinhibitor that inhibits formation of thepolymeric material from the polymeric precursor adjacent to the printwindow.

In some embodiments, the method further comprises, prior to (a),receiving or generating a computer model of the 3D object, wherein theat least the portion of the 3D object is in accordance to the computermodel of the 3D object.

In some embodiments, the build surface is part of a vat that retains thefilm. In some embodiments, the build surface is part of an open platformthat retains the film.

Another aspect of the present disclosure provides a system for printinga three-dimensional (3D) object, comprising: a build surface configuredto retain a film comprising a polymeric precursor; a sensor in sensingcommunication with the build surface; a light source in opticalcommunication with the build surface, wherein the light source isconfigured to provide light; and a controller comprising a circuitoperatively coupled to the sensor and the light source, wherein thecontroller is configured to (i) use the sensor to determine a profile ofthe film, which profile is indicative of a quality of the film, (ii)determine if the profile meets a quality threshold, and (iii) subsequentto (ii), (1) if the profile meets a quality threshold, direct the lightsource to expose at least a portion of the film to the light to initiateformation of a polymeric material from the polymeric precursor, therebyprinting at least a portion of the 3D object, or (2) if the profile doesnot meet the quality threshold, direct the film to be adjusted orredeposited.

In some embodiments, the controller is further configured to (i) exposethe film to an additional light and (ii) use the sensor to detect atleast a portion of the additional light that is transmitted through thefilm.

In some embodiments, the light has a first wavelength and the additionallight has a second wavelength, wherein the second wavelength isdifferent than the first wavelength. In some embodiments, the lightsource is configured to provide the additional light. In someembodiments, the system further comprises an additional light sourceconfigured to provide the additional light.

In some embodiments, the system further comprises an optical diffuserlocated adjacent to the build surface and away from the film, whereinthe optical diffuser is configured to diffuse the additional light.

In some embodiments, during use, the film further comprises a pluralityof particles. In some embodiments, during use, the polymeric precursorencapsulates the plurality of particles. In some embodiments, duringuse, the polymeric material encapsulates the plurality of particles. Insome embodiments, during use, the plurality of particles comprises atleast one metal particle, at least one ceramic particle, or acombination thereof.

In some embodiments, the system further comprises a build headconfigured to move relative to the build surface and hold the at leastthe portion of the 3D object.

In some embodiments, the system further comprises a deposition headadjacent to the build surface and configured to move across the buildsurface to deposit the film adjacent to the build surface. In someembodiments, the build surface comprises a print window configured toretain the film.

In some embodiments, during use, the film further comprises (i) aphotoinitiator that initiates formation of the polymeric material fromthe polymeric precursor away from the print window, and (ii) aphotoinhibitor that inhibits formation of the polymeric material fromthe polymeric precursor adjacent to the print window.

In some embodiments, the build surface is part of a vat that isconfigured to retain the film. In some embodiments, the build surface ispart of an open platform that is configured to retain the film.

Another aspect of the present disclosure provides a non-transitorycomputer readable medium comprising machine executable code that, uponexecution by one or more computer processors, implements any of themethods above or elsewhere herein.

Another aspect of the present disclosure provides a system comprisingone or more computer processors and computer memory coupled thereto. Thecomputer memory comprises machine executable code that, upon executionby the one or more computer processors, implements any of the methodsabove or elsewhere herein.

Additional aspects and advantages of the present disclosure will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only illustrative embodiments of thepresent disclosure are shown and described. As will be realized, thepresent disclosure is capable of other and different embodiments, andits several details are capable of modifications in various obviousrespects, all without departing from the disclosure. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.To the extent publications and patents or patent applicationsincorporated by reference contradict the disclosure contained in thespecification, the specification is intended to supersede and/or takeprecedence over any such contradictory material.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings (also “Figure” and “FIG.” herein), of which:

FIGS. 1A-1D show different configurations of a three-dimensional (3D)printing system.

FIG. 2 shows an example image of a build surface without a film of aviscous liquid.

FIG. 3A shows an example image of a film of a viscous liquid, and FIG.3B shows a respective optical profile of the film of the viscous liquid.

FIG. 4A shows a different example image of a film of a viscous liquid,and FIG. 4B shows a respective optical profile of the film of theviscous liquid.

FIG. 5A shows an example image of a film of a viscous liquid prior toprinting a layer of a 3D object, and FIG. 5B shows an example image of aremainder of the film of the viscous liquid subsequent to printing thelayer of the 3D object.

FIG. 6 shows an example plot of a thickness of a film of a viscousliquid and transmittance of sensor light through the film of the viscousliquid.

FIG. 7 shows an example of a closed loop control of a width of aplurality of films of a viscous liquid.

FIG. 8 shows a computer system that is programmed or otherwiseconfigured to implement methods provided herein.

DETAILED DESCRIPTION

While various embodiments of the invention have been shown and describedherein, it will be obvious to those skilled in the art that suchembodiments are provided by way of example only. Numerous variations,changes, and substitutions may occur to those skilled in the art withoutdeparting from the invention. It should be understood that variousalternatives to the embodiments of the invention described herein may beemployed.

The term “three-dimensional object” (also “3D object”), as used herein,generally refers to an object or a part that is printed by 3D printing.The 3D object may be at least a portion of a larger 3D object or anentirety of the 3D object. The 3D object may be fabricated (e.g.,printed) in accordance with a computer model of the 3D object.

The term “vat,” as used herein, generally refers to a structure (e.g., acontainer, holder, reservoir, etc.) that holds a film (e.g., a layer ofa material) during 3D printing. The material may be a liquid. The filmmay comprise a liquid (e.g., a polymerizable resin or resin mixture)usable for 3D printing. The liquid may have a viscosity that issufficient to permit the liquid to remain on or adjacent to the bottomsurface of the vat. The bottom surface of the vat may be referred to asa build surface (e.g., a print surface). One or more sides of the vat(e.g., a bottom or side surface) may include an optically transparent orsemi-transparent window (e.g., glass or a polymer) to direct lightthrough the window and to the film. The light may be directed to thefilm from a bottom or from one or more sides of the film. In some cases,the window may be precluded. In such a scenario, light may be providedto the film from above the vat.

The term “open platform,” as used herein, generally refers to astructure that supports the film of the liquid (e.g., the filmcomprising the liquid usable for 3D printing) during 3D printing. Theopen platform may be a build surface (e.g., a print surface). The liquidmay have a viscosity that is sufficient to permit the liquid to remainon or adjacent to the open platform during 3D printing. The openplatform may be flat. The open platform may include an opticallytransparent or semi-transparent print window (e.g., glass or a polymer)to direct light through the window and to the film of the liquid. Theopen platform may have various shapes. The open platform may be arectangle or a ring, for example.

The open platform may comprise one or more walls adjacent to the openplatform, such as at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or morewalls. As an alternative, the open platform may comprise at most about10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 wall, or no walls. In some cases, thewalls may enclose the open platform. During printing, a property (e.g.,viscosity) of the liquid used for printing may be sufficient to keep thefilm of the liquid adjacent to the open platform without sufficient flowof the film of the liquid towards the one or more walls. In someexamples, the walls prevent flow of the film of the liquid out of theopen platform. In some cases, sides of the film of the liquid may not bein contact with any objects (e.g., one or more walls) during formationof the at least the portion of the 3D object.

The open platform may not have a side wall.

The open platform may include one or more sides (e.g., side walls) thatare not bounded. For example, the open platform may not be vat or acontainer. The open platform may not be part of a vat or a container.The open platform may be a substrate or slab that does not have adepression (e.g., vat or container) for retaining a liquid. In suchsituations, the liquid may be sufficiently viscous such that the liquidremains on the open platform.

The term “film,” as used herein” generally refers to a layer of amaterial (e.g., a viscous liquid) that is usable to print a 3D object.The film may have a uniform or non-uniform thickness across the film.The film may have an average thickness or a variation of the thicknessthat is below, within, or above a defined threshold (e.g., a value or arange). The average thickness or the variation of the thickness of thefilm may be detectable and/or adjustable during the 3D printing. Anaverage (mean) thickness of the film may be an average of thicknessesfrom at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 100,200, 300, 400, 500, 1000, 2000, 3000, 4000, 5000, or more positionswithin the film. An average (mean) thickness of the film may be anaverage of thicknesses from at most about 5000, 4000, 3000, 2000, 1000,500, 400, 300, 200, 100, 50, 40, 30, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2,or 1 position within the film. A variation of the thickness of the filmmay be a variance (i.e., sigma squared or “σ²”) or standard deviation(i.e., sigma or “σ”) within a set of thicknesses from the at least about2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 100, 200, 300, 400, 500,1000, 2000, 3000, 4000, 5000, or more positions within the film. Avariation of the thickness of the film may be a variance or standarddeviation within a set of thicknesses from the at most about 5000, 4000,3000, 2000, 1000, 500, 400, 300, 200, 100, 50, 40, 30, 20, 15, 10, 9, 8,7, 6, 5, 4, 3, 2, or 1 position within the film.

During 3D printing, one or more parameters (e.g., a speed of depositionof the film adjacent to a surface of the vat or the open platform, aspeed of extrusion of the liquid from a nozzle onto the surface of thevat or the open platform, an amount of the liquid extruded onto thesurface of the vat or the open platform, intensity and/or exposure timeof one or more lights from one or more light sources, etc.) may bemaintained or adjusted to maintain or improve print quality (e.g., aquality of the film prior to printing at least a portion of the 3Dobject, or the printed portion of the 3D object).

The film of the material that is usable to print the 3D object may ormay not be re-deposited (e.g., adjacent to a surface of the vat or theopen platform) prior to printing at least a portion of the 3D object. Insome cases, the film of the material that is usable to print the 3Dobject may be removed and a new film of the material may be re-depositedprior to printing at least a portion of the 3D object. The material fromthe removed film may or may not be recycled to deposit the new film. Insome examples, the film may be re-deposited until a desired (e.g.,pre-determined) thickness, average thickness, or a variation of thethickness is obtained.

The material of the film may be a viscous liquid. In some cases, theviscous liquid may be referred to as a resin. An amount of the viscousliquid in the film of the viscous liquid that is deposited on the buildsurface may be adjustable during the 3D printing. The amount of theviscous liquid in the film may be detectable and/or adjustable duringthe 3D printing. In an example, an amount of the viscous liquid in afirst film deposited to print a first layer of the 3D object may be thesame or different than an amount of the viscous liquid in a second filmdeposited to print a second layer of the 3D object.

The viscous liquid may be dispensed from a nozzle and over a printwindow. The viscous liquid may have a viscosity sufficient to beself-supporting on the print window without flowing or sufficientflowing. A self-supporting film of the viscous liquid may not need oneor more walls to support the film from one or more sides of the film.The self-supporting film of the viscous liquid may be capable ofretaining a thickness and/or a shape of the film for a given amount oftime (e.g., 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more minutes)without one or more walls to support the film from one or more sides ofthe film. The viscosity of the viscous liquid may range between about4,000 centipoise (cP) to about 2,000,000 cP. The viscous liquid may bepressed (e.g., by a blade or a build head) into a film of the viscousliquid on or over the print window. A thickness of the film of theviscous liquid may be adjustable. The viscous liquid may include aphotoactive resin. The photoactive resin may include a polymerizableand/or cross-linkable component (e.g., a polymeric precursor) and aphotoinitiator that activates curing of the polymerizable and/orcross-linkable component, to thereby subject the polymerizable and/orcross-linkable component to polymerization and/or cross-linking. Thephotoactive resin may include a photoinhibitor that inhibits curing ofthe polymerizable and/or cross-linkable component.

In some examples, the viscous liquid may include a plurality ofparticles (e.g., metal, non-metal, or both)—in such a case, the viscousliquid may be a slurry or a photopolymer slurry. The viscous liquid maybe a paste. The plurality of particles may be added to the viscousliquid. The plurality of particles may be solids or semi-solids (e.g.,gels). Examples of non-metal material include ceramic, polymeric, orcomposite material. The plurality of particles may be suspendedthroughout the viscous liquid. The plurality of particles in the viscousliquid may have a distribution that is monodisperse or polydisperse. Insome examples, the viscous liquid may contain additional opticalabsorbers and/or non-photoreactive components (e.g., fillers, binders,plasticizers, etc.). The 3D printing may be performed with at least 1,2, 3, 4, 5, 6, 7, 8, 9, 10 or more viscous liquids. A plurality ofviscous liquids comprising different materials (e.g., differentphotoactive resin and/or different plurality of particles) may be usedfor printing a multi-material 3D object.

When a film of the viscous liquid is deposited (e.g., adjacent to abuild surface of the vat or the open platform), the plurality ofparticles may be suspended throughout the film in a monodispersedistribution or a polydisperse distribution. The plurality of particlesmay be suspended across a line parallel to the build surface in amonodisperse distribution (e.g., a uniform density) or a polydispersedistribution (e.g., a non-uniform density). The plurality of particlesmay be suspected across a thickness or height of the film in amonodisperse distribution or a polydisperse distribution. A density ofthe plurality of particles across the thickness (e.g., along a z-axisperpendicular to the print surface) of the film at two or more positionsacross a surface (e.g., on a xy-plane parallel to the print surface) ofthe film may be uniform or non-uniform. Polydisperse distribution of theplurality of particles across the thickness of the film may be a resultof the film deposition process and/or gravity that pulls down theplurality of particles within the film.

The term “particles,” as used here, generally refers to any particulatematerial that may be melted or sintered (e.g., not completely melted).The particulate material may be in powder form. The particles may beinorganic materials. The inorganic materials may be metallic (e.g.,aluminum or titanium), intermetallic (e.g., steel alloys), ceramic(e.g., metal oxides) materials, or any combination thereof. In somecases, the term “metal” or “metallic” may refer to both metallic andintermetallic materials. The metallic materials may includeferromagnetic metals (e.g., iron and/or nickel). The particles may havevarious shapes and sizes. For example, a particle may be in the shape ofa sphere, cuboid, or disc, or any partial shape or combination of shapesthereof. The particle may have a cross-section that is circular,triangular, square, rectangular, pentagonal, hexagonal, or any partialshape or combination of shapes thereof. Upon heating, the particles maysinter (or coalesce) into a solid or porous object that may be at leasta portion of a larger 3D object or an entirety of the 3D object. The 3Dprinting may be performed with at least about 1, 2, 3, 4, 5, 6, 7, 8, 9,10 or more types of particles. As an alternative, the 3D printing may beperformed with less than or equal to about 10, 9, 8, 7, 6, 5, 4, 3, 2,or 1 particle, or no particles.

The term “deposition head,” as used herein, generally refers to a partthat may move across an open platform. The deposition head may moveacross the open platform and deposit a film of a viscous liquid over aprint window of the open platform. The film of the viscous liquid mayhave a uniform thickness across the print window. The thickness of thefilm may be adjustable. The deposition head may be coupled to a motionstage adjacent to the open platform. The deposition head may have atleast one nozzle to dispense at least one liquid (e.g., viscous liquid)over the print window. The deposition head may have at least one wiperto form the layer of the viscous liquid or remove any excess viscousliquid from the print window. The deposition head may have at least oneactuator to adjust a distance between the at least one wiper the printwindow. In some examples, the deposition head may have a slot die. Thedeposition head may retrieve any excess viscous liquid from the printwindow, contain the excess resin within the deposition head, and/orrecycle the retrieved viscous liquid when printing subsequent portionsof the 3D object. The deposition head may clean the print window.

The 3D printing may be performed with at least 1, 2, 3, 4, 5, 6, 7, 8,9, 10 or more deposition heads. Each of a plurality of deposition headsmay be in fluid communication with a separate source of viscous liquid.The plurality of deposition heads may be used to deposit and curealternating films of different viscous liquids (e.g., differentphotoactive resins and/or different inorganic particles).Compartmentalizing different viscous liquids in separate sources andseparate deposition heads may improve printing speed and preventcross-contamination of the different viscous liquids.

The term “nozzle,” as used herein, generally refers to a component ofthe deposition head that directs the viscous liquid towards the openplatform comprising the window. The nozzle may include an opening forthe viscous liquid to enter and an additional opening for the viscousliquid to exit. In some cases, the nozzle may not comprise anycontraction or control mechanism to adjust flow of the viscous liquidtowards the open platform. In some cases, the nozzle may comprise acontraction or control mechanism to adjust the flow of the viscousliquid towards the open platform.

The term “wiper,” as used herein, generally refers to a part that may bein contact with a print window of an open platform, a viscous liquid, oranother wiper. In some examples, the wiper may be a component of adeposition head. The wiper may be in contact with a viscous liquid topress the viscous liquid into a film. The wiper may be in contact withthe print window to remove any excess viscous liquid. A distance betweenthe wiper and the print window may be adjustable. In some examples, thewiper may be a component in a cleaning zone. The wiper may be in contactwith another wiper to remove any excess viscous liquid. The wiper mayhave various shapes, sizes, and surface textures. The wiper may be ablade (e.g., a squeegee blade, a doctor blade), roller, or rod (e.g.,wire wound rod), for example. The 3D printing may be performed with atleast 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more wipers. In some cases, theblade is part of the nozzle or attached to the nozzle.

In some cases, one or more lights (e.g., from one or more light sources)may be used to initiate (activate) curing of a portion of the film,thereby to print at least a portion of the 3D object. In some cases, oneor more lights (e.g., from one or more light sources) may be used toinhibit (prevent) curing of a portion of the film adjacent to a surfaceof the film (e.g., a surface adjacent to one or more sides of the vat ora surface of the open platform). In some cases, one or more lights(e.g., from one or more light sources) may be used by one or moresensors to determine a profile and/or quality of the film.

The 3D printing may be performed with one wavelength. The 3D printingmay be performed with at least about 2, 3, 4, 5, 6, 7, 8, 9, 10 or morewavelengths that are different. The 3D printing may be performed with atleast about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more lights. The 3Dprinting may be performed with at least about 1, 2, 3, 4, 5, 6, 7, 8, 9,10 or more light sources, and it may be desirable to prevent curing of aportion of the film adjacent to the surface of the film.

The one or more lights may comprise electromagnetic radiation. The term“electromagnetic radiation,” as used herein, generally refers to one ormore wavelengths from the electromagnetic spectrum including, but notlimited to x-rays (about 0.1 nanometers (nm) to about 10.0 nm; or about10¹⁸ Hertz (Hz) to about 10¹⁶ Hz), ultraviolet (UV) rays (about 10.0 nmto about 380 nm; or about 8×10¹⁶ Hz to about 10¹⁵ Hz), visible light(about 380 nm to about 750 nm; or about 8×10¹⁴ Hz to about 4×10¹⁴ Hz),infrared (IR) light (about 750 nm to about 0.1 centimeters (cm); orabout 4×10¹⁴ Hz to about 5×10¹¹ Hz), and microwaves (about 0.1 cm toabout 100 cm; or about 10⁸ Hz to about 5×10¹¹ Hz).

The one or more light sources may comprise an electromagnetic radiationsource. The term “electromagnetic radiation source,” as used herein,generally refers to a source that emits electromagnetic radiation. Theelectromagnetic radiation source may emit one or more wavelengths fromthe electromagnetic spectrum.

The term “photoinitiation,” as used herein, generally refers to aprocess of subjecting a portion of a film of a liquid (e.g., viscousliquid) to a light to cure a photoactive resin in the portion of thefilm of the liquid. The light (photoinitiation light) may have awavelength that activates a photoinitiator that initiates curing of apolymerizable and/or cross-linkable component in the photoactive resin.

The term “photoinhibition,” as used herein, generally refers to aprocess of subjecting a portion of a film of a liquid (e.g., a viscousliquid) to a light to inhibit curing of a photoactive resin in theportion of the film of the liquid. The light (photoinhibition light) mayhave a wavelength that activates a photoinhibitor that inhibit curing ofa polymerizable and/or cross-linkable component in the photoactiveresin. The wavelength of the photoinhibition light and anotherwavelength of a photoinitiation light may be different. In someexamples, the photoinhibition light and the photoinitiation light may beprojected from the same optical source. In some examples, thephotoinhibition light and the photoinitiation light may be projectedfrom different optical sources.

The term “sensor,” as used herein, generally refers to a device or asystem that provides a feedback (e.g., light absorption spectroscopy,image, video, etc.) indicative of the 3D printing process, e.g., afeedback indicative of the film of the viscous liquid on the buildsurface. The sensor may be operatively coupled to a controller (e.g., acomputer) that controls one or more operations (e.g., depositing thefilm of the viscous liquid onto the build surface) of the 3D printing.The controller may adjust the one or more operations of the 3D printing,based on the feedback provided by the sensor. The controller may adjustthe operation(s) during the 3D printing, and thus such feedback may be aclosed loop feedback. The sensor may provide the feedback (i) duringcalibration of the 3D printing system, (ii) prior to, during, and/orsubsequent to depositing the film of the viscous liquid to be used for3D printing, and/or (iii) prior to, during, or subsequent to solidifying(curing) at least a portion of the film of the viscous liquid to printat least a portion of the 3D object. The sensor may provide the feedbackpre-fabrication or post-fabrication of the 3D object. The 3D printingmay use at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more sensors.The 3D printing may use at most about 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1sensor.

Examples of the sensor may comprise a detector, vision system, computervision, machine vision, imager, camera, electromagnetic radiation sensor(e.g., IR sensor, color sensor, etc.), proximity sensor, densitometer(e.g., optical densitometer), profilometer, spectrometer, pyrometer,force sensor (e.g., piezo sensor for pressure, acceleration,temperature, strain, force), motion sensor, magnetic field sensor (e.g.,microelectromechanical systems), electric field sensor, chemical sensor,structured-light sensor, etc.

The sensor may be capable of detecting and/or analyzing one or moreprofiles of various components of the 3D printing system. The variouscomponents may be used (e.g., the print window) and/or generated (e,g.,the film of viscous liquid) during the 3D printing process. The term“profile,” as used herein, generally refers to a view (e.g., image orvideo) and/or electromagnetic spectrum with respect to such components.The view may be a side view, bottom-up view, or top-down view. The viewmay comprise an outline, silhouette, contour, shape, form, figure,structure of the components. The electromagnetic spectrum may beabsorption, emission, and/or fluorescence spectrum of at least a portionof the electromagnetic radiation (e.g., IR radiation). The profiles maybe indicative of one or more features of the components. In an example,the sensor may be capable of sensing or detecting and/or analyzingzero-dimensional (e.g., a single point), one-dimensional (1D),two-dimensional (2D), and/or 3D profiles (e.g., features) of thecomponents.

The sensor may capture profiles of the build surface (e.g., a portion ofthe vat or the open platform), a surface of the build head that isconfigured to hold at least a portion of the 3D object during printing,or a surface of a previously deposited layer of the 3D object adjacentto the build head.

The feedback from the sensor may be one or more images of the film ofthe viscous liquid or any excess viscous liquid remaining on the buildsurface after printing at least a portion of the 3D object. The feedbackfrom the sensor may be one or more videos (e.g., for a duration of time)of the film of the viscous liquid or the excess viscous liquid remainingon the build surface.

The feedback provided by the sensor may comprise one or more internal orexternal features (e.g., temperature, transparency or opacity, surfacetexture, thickness, shape, size, length, area, pattern, density of oneor more particles embedded in the film, defects, etc.) of the filmdeposited on or adjacent to the build surface. In an example, the sensorprovides such feedback of the film prior to solidifying (e.g., curing,polymerizing, cross-linking) a portion of the film into at least aportion of the 3D object. In another example, the sensor provides suchfeedback of any excess viscous liquid remaining on the print surfaceafter the portion of the film is solidified (e.g., cured, polymerized,cross-linked) into the at least a portion of the 3D object and removedfrom the build surface (e.g., by the build head). The feedback maycomprise the one or more internal or external features of at least aportion of a 3D object printed on the build head, or a portion of anon-printed 3D object on the build head onto which at least a portion ofa 3D object is to be printed.

The sensor may be capable of measuring an energy that is emitted,reflected, or transmitted by a medium (e.g., the film of the viscousliquid on the build surface). The sensor may be capable of measuring anenergy density, comprising: electromagnetic energy density, opticalenergy density, reflectance density, transmittance density, absorbancedensity, spectral density, luminescence (fluorescence, phosphorescence)density, and/or electron density. Such energy density may be indicativeof an amount, concentration, and/or density of one or more components(e.g., one or more particles) within one or more points, lines, or areaswithin the film of the viscous liquid.

The sensor may be operatively coupled to a source of energy for sensing,wherein at least a portion of energy for sensing is measured by thesensor as a feedback indicative of the 3D printing process. Such energyfor sensing may be electromagnetic radiation (e.g., from ambient lightor from an electromagnetic radiation source) and/or electrons (e.g.,from an electron beam). In an example, the sensor may be an IR sensor(e.g., an IR camera), and the source of energy may be an IR lightsource. In such a case, the IR sensor may detect at least a portion ofthe IR light from the IR light source that is being reflected by ortransmitted from (i) the film of the viscous liquid adjacent to thebuild surface, or (ii) any excess viscous liquid remaining on the buildsurface. The IR light being reflected by or transmitted from the film ofthe viscous liquid or any excess viscous liquid may be zero-dimensional(a point), 1D (a line), or 2D (a plane).

A single sensor may be operatively coupled to a single source of energyfor sensing. A single sensor may be operatively coupled to at least 2,3, 4, 5, 6, 7, 8, 9, 10, or more sources of energy for sensing that arethe same or different. A single sensor may be operatively coupled to atmost 10, 9, 8, 7, 6, 5, 4, 3, or 2 sources of energy for sensing thatare the same or different. A single source of energy for sensing may beoperatively coupled to at least 2, 3, 4, 5, 6, 7, 8, 9, 10, or moresensors that are the same or different. A single source of energy forsensing may be operatively coupled to at most 10, 9, 8, 7, 6, 5, 4, 3,or 2 sensors that are the same or different.

One or more sensors and one or more sources of energy for sensing may bepart of a same system (e.g., a single enclosed unit) or differentsystems. The one or more sensors may be disposed below, within, on,and/or over the build surface. The one or more sensors and the one ormore sources of energy for sensing may be on a same side or oppositesides of a component of the 3D printing system (e.g., the windowcomprising the build surface, the film of the viscous liquid adjacent tothe build surface, etc.). In some cases, the one or more sensors and theone or more sources of energy may be in contact with the windowcomprising the build surface, the film of the viscous liquid adjacent tothe build surface, and/or any excess viscous liquid remaining on thebuild surface subsequent to printing a layer of the 3D object. In somecases, the one or more sensors and the one or more sources of energy maynot be in contact with the window comprising the build surface, the filmof the viscous liquid adjacent to the build surface, and/or any excessviscous liquid remaining on the build surface subsequent to printing alayer of the 3D object.

The sensor may not be in contact with the film of the viscous liquidwhile generating the feedback. The sensor may be in contact with thefilm of the viscous liquid while generating the feedback.

The sensor and/or the source of energy for sensing may be stationarywith respect to the build surface (e.g., the print window). The sensorand/or the source of energy for sensing may be movable with respect tothe build surface. Such movement may be a relative movement, and thusthe moving piece may be the sensor, the source of energy for sensing,and/or the build surface.

The one or more sensors may be operatively coupled to a controller(e.g., a computer) capable of employing artificial intelligence (e.g.,one or more machine learning algorithms) to analyze a databasecomprising a plurality of feedbacks indicative of various components ofthe 3D printing system, such as the film of the viscous liquid on thebuild surface or of any excess viscous liquid remaining on the buildsurface after printing a portion of the 3D object. One or more machinelearning algorithms of the artificial intelligence may be capable ofdistinguishing or differentiating profiles (e.g., features) of a film ofthe viscous liquid on or adjacent to the build surface based on thedatabase. Such features may comprise the film quality, film thickness,density of one or more components (e.g., one or more particles, etc.) inthe film, or one or more defects (e.g., bubbles, wrinkles,pre-polymerized particulates, etc.).

The database may further comprise a plurality of training data sets thatcomprise example feedback indicative of the features of the film. Theplurality of training data sets may allow the machine learningalgorithm(s) to learn a plurality of parameters to generate one or moremodels (e.g., mathematical models, classifiers) that can be used todistinguish or differentiate the features of a new film of the viscousliquid received from the one or more sensors during the 3D printing. Inan example, the feedback from a sensor may be an optical (e.g., IR)densitometry profile of the film of the viscous liquid. In such a case,the trained machine learning algorithm may be used to distinguish (i) avariation in optical density due to a height defect across the film,(ii) a variation in optical density due to voids (e.g., bubbles,streaks, etc.) in the film, and (iii) a variation in optical density dueto a difference in the density of one or more particles (e.g., metal orceramic particles) in the film.

In some cases, a series of machine learning algorithms may be connectedas an artificial neural network to better recognize, categorize, and/orclassify each feature of the film of the viscous liquid or each featureof any excess viscous liquid remaining on the build surface from thefeedback of the one or more sensors. In some cases, an artificialintelligence system capable of acquiring, processing, and analyzingimage and/or video feedbacks from the one or more sensors, and suchsystem may be referred to as computer vision.

In some cases, the one or more machine learning algorithms may use deeplearning algorithms. The deep learning algorithms may be capable ofgenerating new classifications (e.g., categories, sub-categories, etc.)of one or more features of the viscous liquid or the film of the viscousliquid, based on a new feedback and a database comprising a plurality ofprevious feedbacks and example feedbacks. The deep learning algorithmsmay use the new classifications to distinguish or differentiate thefeatures of the viscous liquid or the film of the viscous liquid.

The term “diffuser,” as used herein, generally refers to a sheet (e.g.,a plate) or a film (e.g., a laminate or coating on an optical lens or awindow) that diffuses energy (e.g., light). The diffuser may scatter orfilter the energy. In some cases, the diffuser may receive one or moreelectromagnetic radiations (e.g., IR lights) on a first side of thediffuser, then transmit scattered (e.g., distributed, evenlydistributed, etc) electromagnetic radiations from a second side of thediffuser opposite the first side. The transmitted scatteredelectromagnetic radiations may form a flood electromagnetic radiation.The diffuser may eliminate bright spots corresponding to location(s) ofone or more electromagnetic radiation sources. In some cases, flux ofthe scattered electromagnetic radiations from the diffuser may beindependent of angle with respect to the diffuser and/or of positionwithin a surface of the diffuser. The diffuser may diffuse the one ormore electromagnetic radiations that are being received by the one ormore sensors, thereby reducing directionality of the one or more lightsensors with respect to the one or more electromagnetic radiationsources. In some cases, the diffuser may cause light to spread evenlyacross a surface (e.g., a surface of the diffuser), thereby minimizingor removing high intensity bright spots as the light travels through thediffuser.

The diffuser may be disposed between the one or more sources of energy(e.g., one or more electromagnetic radiations) for sensing and thecorresponding sensor(s). In an example, the diffuser may diffuse the oneor more electromagnetic radiations (e.g., one or more IR lights) anddirect the scattered electromagnetic radiations towards a build surface(e.g., a print window), to the film of the viscous liquid, and to thecorresponding sensor(s) (e.g., one or more IR sensors). In some cases,the scattered electromagnetic radiations may be directed to the film ofthe viscous liquid without passing through the build surface. In anotherexample, the diffuser may be adjacent to the one or more sensor(s).

The diffuser may be transparent, semi-transparent, semi-opaque, oropaque. The diffuser may be ceramic, polymeric (e.g., polycarbonate,polytetrafluoroethylene (PTFE), etc.), or a combination thereof.Examples of the diffuser comprise a holographic diffuser, a whitediffusing glass, and a ground glass diffuser. Other examples of thediffuser include paper or fabric.

One or more surfaces of the diffuser may comprise a matte finish on itssurface to further assist in scattering the one or more electromagneticradiations. The diffuser may not be a mirror. During the 3D printingprocess, at least about 1, 2, 3, 4, 5, or more diffusers may be used.During the 3D printing process, at most about 5, 4, 3, 2, or 1 diffusermay be used.

The 3D printing system may be surrounded by an enclosure (e.g., a caseor fabric). The enclosure may prevent external energy (e.g., ambientlight) from interfering with one or more lights used during the 3Dprinting.

The term “green body,” as used herein, generally refers to a 3D objectthat has a polymeric material and a plurality of particles (e.g., metal,ceramic, or both) that are encapsulated by the polymeric material. Theplurality of particles may be in a polymer (or polymeric) matrix. Theplurality of particles may be capable of sintering or melting. The greenbody may be self-supporting. The green body may be heated in a heater(e.g., in a furnace) to burn off at least a portion of the polymericmaterial and coalesce the plurality of particles into at least a portionof a larger 3D object or an entirety of the 3D object.

The present disclosure provides methods and systems for forming a 3Dobject. Such methods may employ application of a film of a liquidadjacent to an open platform and exposing the film to light to subjectat least a portion of the film to polymerization and/or cross-linking.The 3D object may be based on a computer model of the 3D object, such asa computer-aided design (CAD) stored in a non-transitory computerstorage medium (e.g., medium).

Methods and Systems for 3D Printing

An aspect of the present disclosure provides a method for printing a 3Dobject. The method may comprise providing, adjacent to a build surface,a film comprising a polymeric precursor. The method may comprise using asensor to determine a profile of the film, which profile is indicativeof a quality of the film. The method may comprise determining if theprofile meets a quality threshold. The method may comprise, if theprofile meets a quality threshold, using a light source to expose atleast a portion of the film to light to initiate formation of apolymeric material from said polymeric precursor, thereby printing atleast a portion of said 3D object. Alternatively, the method maycomprise, if the profile does not meet the quality threshold, adjustingor redepositing said film.

Adjusting the film may comprise redistributing the film. In some cases,the film may be pressed (e.g., by a doctor blade of a deposition head)to redistribute the viscous liquid in the film, thereby to re-flattenthe film and adjust a thickness of the film. In some cases, additionalviscous liquid may be deposited on the film (e.g., by the depositionhead) to fill in defects (e.g., voids) in the film. In some cases,redistributing the film may comprise treating the film with an externalsource of energy (e.g., sound energy) to redistribute one or morecomponents (e.g., one or more particles) in the film. In an example,sound energy may be directed to the film to induce sonication within thefilm, thereby to (i) remove one or more voids in the film, and/or (ii)redistribute one or more particles to adjust the gradient of the one ormore particles in the film.

Redepositing the film may comprise removing at least a portion of thefilm from the build surface and depositing an additional film adjacentto said build surface. In some cases, the at least the portion of thefilm from the build surface may be used to deposit the additional film.In some cases, an additional viscous liquid may be added (e.g., by thedeposition head) to the at least the portion of the film from the buildsurface to deposit the additional film. In some cases, the at least theportion of the film from the build surface may be removed (e.g.,discarded), and new viscous liquid may be used to deposit the additionalfilm.

In some cases, the film may comprise a liquid (e.g., a viscous liquid)that comprises the polymeric precursor. The viscous liquid may be usedfor printing the at least the portion of the 3D object. The viscousliquid may comprise a photoactive resin to form a polymeric material.The photoactive resin may comprise the polymeric precursor of thepolymeric material. The photoactive resin may comprise at least onephotoinitiator that is configured to initiate formation of the polymericmaterial from the polymeric precursor (e.g., initiate formation of thepolymeric material from the polymeric precursor away from the printwindow). The photoactive resin may comprise at least one photoinhibitorthat is configured to inhibit formation of the polymeric material fromthe polymeric precursor (e.g., inhibit formation of the polymericmaterial from the polymeric precursor adjacent to the print window). Thephotoinitiator and the photoinhibitor may be activated by twowavelengths that are different. The two wavelengths for thephotoinitiator and the photoinhibitors, respectively, may be from a sameoptical source or different optical sources. The viscous liquid maycomprise a plurality of particles usable for forming the at least theportion of the 3D object.

The build surface may comprise a print window, and the film comprisingthe polymeric precursor may be provided adjacent to the print window.The build surface (e.g., the build surface comprising the print window)may be part of a vat that retains the film. The build surface may bepart of an open platform configured to hold the film comprising thepolymeric precursor.

At least a portion of the open platform may comprise the window. Thewindow may be the open platform or part of the open platform. Forexample, at least about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or more of open platformmay comprise the window. As another example, at most about 95%, 90%,85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%,15%, 10%, or less of the open platform may comprise the window. In somecases, the open platform may be the window. A surface of the openplatform comprising the window may be flat.

The window may be transparent or semitransparent (translucent). Thewindow may be comprised of an optical window material, such as, forexample, glass or a polymeric material (e.g., polymethylmethacrylate(PMMA)). In some cases, the window may be comprised ofpolydimethylsiloxane (PDMS) that is permeable to oxygen. Duringprinting, the oxygen dissolved in the window may (i) diffuse into acontact surface between the window and the viscous liquid comprising thephotoactive resin (the window-viscous liquid interface) and (ii) inhibitcuring of the photoactive resin at the contact surface. The window maybe positioned above the optical source for photopolymer-based 3Dprinting using bottom-up illumination. As an alternative, the window maybe positioned below the optical source. As another alternative, thewindow may be positioned between a first optical source and a secondoptical source.

The quality of the film comprising the polymeric precursor may bedeterminative of a material or structural quality of the 3D object thatis being printed. The profile of the film may be analyzed (e.g. by thecomputer) to obtain information indicative of the one or more featuresof the film. The quality of the film may be determined by identifyingand/or characterizing one or more features in the film, comprising oneor more dimensions (e.g., height or thickness, width, area, defects,etc.), volume, shape or pattern (e.g., a projectile 2D pattern),temperature, and/or viscosity. The quality of the film may be determinedby identifying and/or characterizing one or more defects in the film(e.g., on a surface of the film, in the film, etc.). Examples of the oneor more defects comprise voids, holes, thinning, thickening, bubbles,lines, wrinkles, phases, foreign artifacts (e.g., dusts), non-uniformdensities of one or more components (e.g., one or more metal ornon-metal particles), and/or pre-polymerized particulates of thepolymeric precursor.

The sensor may be used to determine the quality of the film prior toprinting and/or during printing the at least the portion of the 3Dobject. The quality of the film may be determined optically, e.g., bytaking an image or video of the film by using the sensor. The sensor ora controller (e.g., a computer) operatively coupled to the sensor maycompare such optical feedback (e.g., the image or video of the film) toa reference to determine the quality of the film. The reference may be acomputer model of the film or one or more pre-determined features of thefilm. In some cases, the sensor may comprise or be operatively coupledto artificial intelligence (e.g., a trained machine learning algorithm)to identify the one or more features in the film indicative of the filmquality.

The method of 3D printing may further comprise using the profile of thefilm comprising the polymeric precursor to determine a variation of oneor more profiles of the film. In some cases, an average value and/orvariation (e.g., standard deviation, standard error) of one or morefeatures (e.g., thickness, width(s), area, defects, etc.) of the filmmay be determined (e.g., calculated). Such average value and/orvariation may be compared to a reference (e.g., a threshold value) todetermine the film quality. The reference may be a threshold value thatis pre-determined for the 3D printing process, or pre-determined foreach film comprising the polymeric precursor. The threshold value may bea pre-determined value of the one or more features of the film or apredetermined range of values of the one or more features. In somecases, the threshold may be met when the average value and/or itsvariation is below the threshold value, equal to the threshold value,greater than the threshold value, or any combination thereof. Thethreshold value may be an upper limit value and/or a lower limit valueof the one or more features of the film.

If the variation of the profile of the film meets the threshold value,the at least the portion of the film may be exposed to light to initiateformation of the polymeric material from the polymeric precursor,thereby printing the at least the portion of the 3D object. If thevariation of the profile of the film does not meet the threshold value,the film comprising the polymeric precursor may be removed (e.g., by thedeposition head) from the build surface, and a new film comprising thepolymeric precursor may be deposited on the build surface.

When removing a previously deposited film of a liquid comprising thepolymeric precursor and subsequently depositing a new film of theliquid, the liquid comprising the polymeric precursor from the removedfilm may be re-used to deposit the new film on the build surface.Alternatively or in addition to, an additional liquid comprising thepolymeric precursor may be used (e.g., added) to deposit the new film onthe build surface. In some cases, one or more operations of the 3Dprinting process may or may not be adjusted (e.g., by the controller)prior to depositing the new film on the build surface, based on thesensor's feedback comprising the profile of the film. Such feedback maybe a closed loop feedback. Examples of the operations of the 3D printingprocess that may be adjusted based on the closed loop feedback from thesensor include changing an amount of the liquid comprising the polymericprecursor to be used by the deposition head to deposit the film,changing a source of the liquid comprising the polymeric precursor(e.g., selecting a source from a plurality of sources), changing apre-determined thickness of the film (e.g., changing a distance betweena wiper of the deposition head and the print window), changing a speedof movement of the deposition head during deposition of the film on theprint window, and changing a direction of movement of the depositionhead during deposition of the film (e.g., from left-to-right orright-to-left).

The profile may be a thickness profile of the film, and the qualitythreshold may be an average or variation (e.g., a variance or standarddeviation) of the average thickness of the film. After the filmcomprising the polymeric precursor is deposited at a pre-determinedthickness on a build surface, the sensor may provide an optical feedback(e.g., an image or video based on IR radiation reflected by ortransmitted from the film) and determine (e.g., by the controller) theaverage thickness and/or the variation of the average thickness of thefilm. In some cases, if the determined average and/or variation of thefilm thickness meets the quality threshold (e.g., is equal to or belowthe pre-determined thickness variation value), the 3D printing processmay proceed by exposing the at least the portion of the film to light(e.g., photoinitiation light) to initiate formation of the polymericmaterial from the polymeric precursor, thereby printing the at least theportion of the 3D object. In some cases, if the determined averageand/or variation of the film thickness does not meet the qualitythreshold (e.g., is above the pre-determined thickness variation value),the film may be removed from the build surface (e.g., by the depositionhead) and a new film comprising the polymeric precursor may be deposited(e.g., by the deposition head) on the build surface. Subsequently, thesensor may be used to determine a profile of the new film, which profileis indicative of a quality of the new film. If the profile of the newfilm meets the quality threshold, the 3D printing process may proceed byinitiating formation of a polymeric material from the polymericprecursor in the new film. Such methods described herein may beimplemented to other features of the film, such as, for example, widthof the film, cross-sectional area of the film, or a density of one ormore particles (e.g., metallic or non-metallic particles) in the film.

The sensor may be configured to measure a thickness of a single positionof the film (e.g., a single point on the xy-plane of the film parallelto the print window) comprising the polymeric precursor. In such a case,the sensor may be operated multiple times to measure a plurality ofthicknesses corresponding to a plurality of positions of the film.Alternatively or in addition to, the sensor may be configured to measurea 1D optical profile (e.g. one or more lines), one or more 2D images, orone or more videos of the film and analyze the 1D optical profile,image(s), and/or video(s) to obtain (e.g., by using a computer system),one or more thicknesses of one or more positions of the film.

In some cases, the threshold value of the standard deviation of theaverage film thickness may range between about 0.001 millimeter (mm) toabout 0.1 mm. The threshold value of the standard deviation of theaverage film thickness may be at least about 0.001 mm, 0.002 mm, 0.003mm, 0.004 mm, 0.005 mm, 0.006 mm, 0.007 mm, 0.008 mm, 0.009 mm, 0.01 mm,0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm,0.1 mm, or more. The threshold value of the standard deviation of theaverage film thickness may be at most about 0.1 mm, 0.09 mm, 0.08 mm,0.07 mm, 0.06 mm, 0.05 mm, 0.04 mm, 0.03 mm, 0.02 mm, 0.01 mm, 0.009 mm,0.008 mm, 0.007 mm, 0.006 mm, 0.005 mm, 0.004 mm, 0.003 mm, 0.002 mm,0.001 mm, or less. In some cases, the threshold value of the standarddeviation of the average thickness of the film may range between about0.1 percent (%) to about 20% of the average thickness of the film. Thethreshold value of standard deviation of the average thickness of thefilm may be at least about 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%,0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%,15%, 16%, 17%, 18%, 19%, 20%, 30%, or more. The threshold value ofstandard deviation of the average thickness of the film may be at mostabout 30%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%,8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%,0.3%, 0.2%, 0.1%, or less.

The profile may be a width profile of the film, and the qualitythreshold may be an average or variation of the width of the film. Thewidth may be parallel or perpendicular to a movement of the depositionhead as it moves across the build surface. In an example, the depositionhead may move along the y-axis of the build surface, and a dimension ofthe film along the x-axis of the build surface may be used as the widthof the film. The width of the film may be indicative of a volume of theviscous liquid comprising the polymeric precursor in the film. After thefilm comprising the polymeric precursor is deposited to a pre-determinedarea, the sensor may provide an optical feedback and determine anaverage width of the film. The average width of the film may be measuredin real time as an indication of a volume of the viscous liquiddeposited in the film, and the estimated volume of the viscous liquidmay be used as a closed loop control of the volume of the viscous liquidin the film. As such, the controller may be configured to increaseand/or decrease an amount of the viscous liquid to be deposited for asubsequent film of the viscous liquid to adhere to a pre-determinedsetting of the volume of the viscous liquid.

In some cases, if the determined average film width meets the qualitythreshold (e.g., is equal to or greater than the pre-determined filmwidth), the 3D printing process may proceed by initiating formation of apolymeric material from the polymeric precursor in the film. In somecases, if the determined average film width does not meet the qualitythreshold (e.g., less than the pre-determined film width), the filmcomprising the polymeric precursor may be removed and a new filmcomprising the polymeric precursor may be deposited. The viscous liquidfrom the removed film and an additional amount of the viscous liquid(e.g., from a nozzle in fluid communication with a source of the viscousliquid) may be combined to deposit the new film, such that the new filmmay meet the film width quality threshold. In some cases, if thedetermined average film width does not meet the quality threshold (e.g.,less than the pre-determined film width), but the film is determined tobe sufficient for printing at least a portion of the 3D object, the 3Dprinting process may proceed by initiating formation of a polymericmaterial from the polymeric precursor in the film. When depositing a newlayer of the film for a subsequent portion of the 3D object to beprinted, an amount of the viscous liquid to be used for the new layermay be adjusted (e.g., increased), such that the new film may meet thefilm width quality threshold.

In some cases, the determined average film width may not meet thequality threshold by exceeding a pre-determined range of the width ofthe film. In such a case, the 3D printing process may be adjusted toreduce the additional amount of the viscous liquid (e.g., from thenozzle in fluid communication with the source of the viscous liquid)that is to be added in printing one or more subsequent portions (e.g.,layers) of the 3D object.

Alternatively or in addition to, an area (e.g., a projectile area)and/or shape of the film may be used in place of the width of the filmto assess film quality.

A relationship between (i) the width or area of the film and (ii) thevolume of the viscous liquid in the film may be defined by a factor(e.g. a constant value). The relationship may assume a constantthickness of the film (e.g., about 50 micrometer (m)). The factor may beused to convert (i) the width or area of the film to (ii) the volume ofthe viscous liquid in the film. The factor may be used by the controllerto determine an amount of the viscous liquid in the film prior to and/orsubsequent to printing at least a portion (e.g., a layer) of the 3Dobject. The factor may be used by the controller to determine an amountof the viscous liquid to be added to or removed when depositing a newfilm of the viscous liquid. In some cases, the factor may be used by thecontroller to determine an amount of the viscous liquid to be added toor removed from the amount that may otherwise be dispensed onto thebuild surface to print the new film of the viscous liquid. The factormay be a pre-determined value at a pre-determined constant thickness(e.g., 0.01 milliliter (mL) of viscous liquid per 1 mm of film width, or0.01 mL of viscous liquid per 1 mm² of film area). The factor may beuniversal for a plurality of different viscous liquids (e.g., differentcompositions) or specific for each type of viscous liquid.

In some cases, the factor may range from about 0.0001 mL/mm to about 1mL/mm. The factor may range from at least about 0.0001 mL/mm, 0.0002mL/mm, 0.0003 mL/mm, 0.0004 mL/mm, 0.0005 mL/mm, 0.006 mL/mm, 0.0007mL/mm, 0.0008 mL/mm, 0.0009 mL/mm, 0.001 mL/mm, 0.002 mL/mm, 0.003mL/mm, 0.004 mL/mm, 0.005 mL/mm, 0.006 mL/mm, 0.007 mL/mm, 0.008 mL/mm,0.009 mL/mm, 0.01 mL/mm, 0.02 mL/mm, 0.03 mL/mm, 0.04 mL/mm, 0.05 mL/mm,0.06 mL/mm, 0.07 mL/mm, 0.08 mL/mm, 0.09 mL/mm, 0.1 mL/mm, 0.2 mL/mm,0.3 mL/mm, 0.4 mL/mm, 0.5 mL/mm, 0.6 mL/mm, 0.7 mL/mm, 0.8 mL/mm, 0.9mL/mm, 1 mL/mm, or more. The factor may range from at most about 1mL/mm, 0.9 mL/mm, 0.8 mL/mm, 0.7 mL/mm, 0.6 mL/mm, 0.5 mL/mm, 0/4 mL/mm,0.3 mL/mm, 0.2 mL/mm, 0.1 mL/mm, 0.09 mL/mm, 0.08 mL/mm, 0.07 mL/mm,0.06 mL/mm, 0.05 mL/mm, 0.04 mL/mm, 0.03 mL/mm, 0.02 mL/mm, 0.01 mL/mm,0.009 mL/mm, 0.008 mL/mm, 0.007 mL/mm, 0.006 mL/mm, 0.005 mL/mm, 0.004mL/mm, 0.003 mL/mm, 0.002 mL/mm, 0.001 mL/mm, 0.0009 mL/mm, 0.0008mL/mm, 0.0007 mL/mm, 0.0006 mL/mm, 0.0005 mL/mm, 0.0004 mL/mm, 0.0003mL/mm, 0.0002 mL/mm, 0.0001 mL/mm, or less.

In some cases, the factor may range from about 0.0001 mL/mm² to about 1mL/mm². The factor may range from at least about 0.0001 mL/mm², 0.0002mL/mm², 0.0003 mL/mm², 0.0004 mL/mm², 0.0005 mL/mm², 0.006 mL/mm²,0.0007 mL/mm², 0.0008 mL/mm², 0.0009 mL/mm², 0.001 mL/mm², 0.002 mL/mm²,0.003 mL/mm², 0.004 mL/mm², 0.005 mL/mm², 0.006 mL/mm², 0.007 mL/mm²,0.008 mL/mm², 0.009 mL/mm², 0.01 mL/mm², 0.02 mL/mm², 0.03 mL/mm², 0.04mL/mm², 0.05 mL/mm², 0.06 mL/mm², 0.07 mL/mm², 0.08 mL/mm², 0.09 mL/mm²,0.1 mL/mm², 0.2 mL/mm², 0.3 mL/mm², 0.4 mL/mm², 0.5 mL/mm², 0.6 mL/mm²,0.7 mL/mm², 0.8 mL/mm², 0.9 mL/mm², 1 mL/mm², or more. The factor mayrange from at most about 1 mL/mm², 0.9 mL/mm², 0.8 mL/mm², 0.7 mL/mm²,0.6 mL/mm², 0.5 mL/mm², 0/4 mL/mm², 0.3 mL/mm², 0.2 mL/mm², 0.1 mL/mm²,0.09 mL/mm², 0.08 mL/mm², 0.07 mL/mm², 0.06 mL/mm², 0.05 mL/mm², 0.04mL/mm², 0.03 mL/mm², 0.02 mL/mm², 0.01 mL/mm², 0.009 mL/mm², 0.008mL/mm², 0.007 mL/mm², 0.006 mL/mm², 0.005 mL/mm², 0.004 mL/mm², 0.003mL/mm², 0.002 mL/mm², 0.001 mL/mm², 0.0009 mL/mm², 0.0008 mL/mm², 0.0007mL/mm², 0.0006 mL/mm², 0.0005 mL/mm², 0.0004 mL/mm², 0.0003 mL/mm²,0.0002 mL/mm², 0.0001 mL/mm², or less.

The method of 3D printing may further comprise (i) exposing the filmcomprising the polymeric precursor to an additional light (i.e., thesensor light) and (ii) using the sensor to detect at least a portion ofthe additional light that is transmitted through the film. The sensorand a source of the sensor light may be disposed on a same side (e.g.,on a same surface of the print window) or on opposite sides (e.g., onopposite surfaces of the print window) of the film. In an example, thesensor light may be directed from a first side of the print window andtowards the print window (e.g., transparent or semi-transparent glass orpolymer), transmitted through the print window and into the film on oradjacent to a second side of the print window opposite the first side,and transmitted through the film and into the sensor disposed adjacentto (e.g., above) the film and on the second side of the print window.

Alternatively or in addition to, the method of 3D printing may furthercomprise (i) exposing the film to the sensor light and (ii) using thesensor to detect at least a portion of the sensor light that isreflected by the film. The sensor and a source of the sensor light maybe disposed on a same side (e.g., a same surface) of the film. In somecases, the sensor light may be directed towards an exposed surface ofthe film, and the film may reflect at least a portion of the sensorlight back through the exposed surface of the film and to the sensor.The exposed surface may be a top surface of the film away from the buildsurface, or one or more vertical sides of the film not in contact withthe build surface. In some cases, the sensor light may be directedthrough the build surface (e.g., the print window) and to the film, andthe film may reflect at least a portion of the sensor light back throughthe build surface and to the sensor disposed adjacent to (e.g., below)the build surface and away from the film.

The controller may be configured to convert transmittance, opticaldensity or absorbance, and/or reflectance of the sensor light into aprofile of the film (e.g., thickness, volume, etc.). The transmittancemay be defined as the ratio of the light transmitted through the film tothe light incident upon it. The optical density or absorbance may bedefined as the logarithm of the reciprocal of the transmittance. Thereflectance may be defined as the ratio of the light reflected from thefilm to the light incident upon it. In an example, films with differentknown and verified thicknesses may be printed to obtain a film thicknesstransmittance and/or reflectance of the sensor light. Subsequently, thethickness vs. sensor light transmittance/reflectance plot may be used toconvert any future detection of the sensor lighttransmittance/reflectance into a respective film thickness.

The optical feedback of the sensor may be an optical profile (e.g., a 2Doptical image and/or video) of the film of the viscous liquid or aportion thereof. The optical profile may be transmittance of the sensorlight through the film of the viscous liquid and/or reflectance of thesensor light by the film of the viscous liquid. The controlleroperatively in communication with the sensor may be configured toquantitatively measure optical density of the transmitted and/orreflected sensor light in the optical profile of the film, therebygenerating a densitometry of the film. Thus, the sensor, the sensorlight source that is configured to provide the sensor light, and thecontroller may serve as a densitometer to measure 0D, 1D, 2D, and/or 3Doptical density of the film. The optical density of the film may beindicative of the density of one or more components in the film, suchas, for example, one or more particles in the film. While a profilometermay be able to provide a surface profile (e.g., smoothness, roughness,etc.) of the film of the viscous liquid, the profilometer may not beable to provide the optical density of the film of the viscous liquid.

The light (i.e., photoinitiation light) to initiate formation of thepolymeric material from the polymeric precursor may have a firstwavelength, and the additional light (i.e., sensor light) for the sensormay have a second wavelength. In some cases, the second wavelength maybe different than the first wavelength. In some cases, thephotoinitiation light may comprise wavelengths ranging between about 420nanometers (nm) to about 510 nm. In an example, the first wavelength toinduce photoinitiation is about 460 nm. In some cases, the additionallight may comprise IR wavelengths ranging between about 700 nm to about1000 nm. In some cases, the additional light may comprise a IRwavelength of about 850 nm. In an example, the additional light maycomprise (i) near IR wavelengths ranging between about 700 nm to about1.5 micrometer (μm), (ii) medium IR wavelengths ranging between about1.5 μm to about 4 μm, (iii) and/or far IR wavelengths ranging betweenabout 4 μm to about 1 millimeter. In some cases, the additional lightmay comprise the visible red wavelengths ranging between about 620 nm toabout 700 nm.

In some cases, the light for photoinitiation and the additional lightfor the sensor may be provided by a same light source (e.g., adual-wavelength projector, such as a dual-wavelength laser). Such lightsource may be adjacent to the build surface (e.g., the print window) andaway from the film comprising the polymeric precursor. Alternatively orin addition to, such light source may be disposed on a same side of thebuild surface as the film comprising the polymeric precursor.

In some cases, the light for photoinitiation may be provided by a lightsource (i.e., a photoinitiation light source), and the additional lightfor the sensor may be provided by an additional light source (i.e., asensor light source). The photoinitiation light source and the sensorlight source may be different. In an example, the photoinitiation lightsource and the sensor light source are different. The photoinitiationlight source and the sensor light source may be on a same side oropposite sides of the build surface. The photoinitiation light sourceand/or the sensor light source may be adjacent to the build surface(e.g., print window) and away from the film comprising the polymericprecursor. Alternatively or in addition to, the photoinitiation lightsource and/or the sensor light source may be disposed on a same side ofthe build surface as the film comprising the polymeric precursor.

The method of 3D printing may further comprise using a diffuser (e.g.,an optical diffuser), located adjacent to the build surface (e.g., printwindow) and away from the film comprising the polymeric precursor, todiffuse the additional light (i.e., the sensor light). In some cases,sensor light source (e.g., the radiation source) may direct the sensorlight (e.g., IR radiation) towards the diffuser, and the diffuser mayscatter at least a portion of the IR radiation and direct the scatteredsensor light towards the film comprising the polymeric precursor.Alternatively or in addition to, the diffuser maybe located adjacent tothe film comprising the polymeric precursor and away from the buildsurface.

The diffuser may be stationary with respect to the build surface (e.g.,the print window). The diffuser may be movable with respect to the buildsurface. Such movement may be a relative movement, and thus the movingpiece may be the diffuser and/or the build surface. The diffuser may bestationary with respect to the additional light source (i.e., the sensorlight source). The diffuser may be movable with respect to theadditional light source. Such movement may be a relative movement, andthus the moving piece may be the diffuser and/or the additional lightsource. The diffuser may be configured to move parallel and/or verticalto the build surface. In some cases, the diffuser may be configured tomove at least in a linear or non-linear (e.g., circular) direction thatis parallel to the build surface. In some cases, the diffuser may bemoved away from the build surface such that the diffuser does notinterfere with the path of the light (i.e., the photoinitiation light)from the light source and towards the film of polymeric precursordisposed on or adjacent to the build surface. As such, in some cases,the diffuser may be mechanically coupled to various mechanicalstructures (e.g., motors) for moving the diffuser in a direction towardsor away from the path of the light. The various mechanical structuresmay be configured to move the diffuser in a direction towards or awayfrom the build surface.

At least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more diffusers may beused to diffuse the additional light. At most about 10, 9, 8, 7, 6, 5,4, 3, 2, or 1 diffuser may be used to diffuse the additional light. Whenusing a plurality of diffusers, the plurality of diffusers may or maynot be disposed on top of each other. The plurality of diffusers maymove relative to each other.

The profile of the film comprising the polymeric precursor may be anoptical profile (i.e., densitometry). The optical profile may becomprised of at least a portion of the electromagnetic radiation (e.g.,at least a portion of IR radiation). The profile of the film may be azero-dimensional (e.g., individual point or xy-coordinate in the film),1D (e.g., a line parallel or perpendicular to the build surface), 2D(e.g., a plane parallel or perpendicular to the build surface), and/or3D (e.g., one or more voxels in the film). In some cases, the profilemay be a 2D profile. In some cases, the method may further compriseusing the profile to determine a cross-sectional dimension of the film.The cross-sectional dimension of the film may be parallel,perpendicular, or angled (e.g., not parallel or perpendicular) to thebuild surface.

The film comprising the polymeric precursor may further comprise aplurality of particles, and the profile may be a density profile of theplurality of particles in the film. The plurality of particles maycomprise at least one metal particle, at least one ceramic particle, ora combination thereof. Upon solidifying (e.g., curing, cross-linking) atleast a portion of the polymeric precursor in the film into a polymericmaterial, the polymeric material may encapsulate one or more of theplurality of particles.

The method may comprise providing a build head for holding at least aportion of the 3D object. Prior to directing the light through the printwindow and to the film of the viscous liquid, the method may furthercomprise moving the build head towards the print window and bringing incontact with the film of the viscous liquid. Subsequent to directing thelight to cure at least a portion of the photoactive resin in the film ofviscous liquid between the print window and the build head, the methodmay further comprise moving the build head in a direction away from theprint window. In some cases, the method may further comprise moving thebuild head in the direction away from the window while forming the 3Dobject. The rate of movement of the build head may be controlled toadjust a thickness of one or more layers in the 3D object. A surface ofthe build head in contact with a first layer of the 3D object may besmooth, knurled, or serrated to adjust contact surface area and/orfrictional force between the surface and the first layer of the 3Dobject. Alternatively or in addition to, the first layer of the 3Dobject may be a support layer for the 3D object that may be removedpost-processing.

The method may further comprise using a build head. The build head maybe configured to hold and/or support at least a portion (e.g., a layer)of the 3D object. During printing, the at least the portion of the 3Dobject may be printed on the build head. The build head may beconfigured to move relative to the print window during printing. Thebuild head may be configured to move along a direction away from theprint window during printing. Such movement may be relative movement,and thus the moving piece may be the build head, the print window, orboth. In some cases, the build head may be connected to a build headactuator for moving the build head relative to the print window. Thebuild head actuator may be a mechanical, hydraulic, pneumatic, orelectro-mechanical actuator. Alternatively or in addition to, the openplatform comprising the print window may be connected to an openplatform actuator for moving the open platform relative to the buildhead. The open platform actuator may be a mechanical, hydraulic,pneumatic, or electro-mechanical actuator. The controller may beoperatively coupled to the build head actuator and/or the open platformactuator to control the relative distance between the build head and theprint window. The relative distance between the build head and the printwindow may be adjusted to adjust a thickness of a layer within the atleast the portion of the 3D object.

The method may further comprise exposing the at least the portion of thefilm to the light to initiate formation of the polymeric material fromthe polymeric precursor with a build head in contact with the film. Themethod may further comprise moving the build head away from the buildsurface. Subsequently, the method may further comprise using the sensorto measure an additional profile (e.g., optical profile) of the filmadjacent to the build surface. The additional profile of the film may bea profile of any excess of the film that is remaining on the buildsurface after printing a previously deposited portion (e.g., layer) ofthe 3D object. The additional profile may be a negative or invertedprofile (e.g., a negative or inverted optical profile) of the at leastthe portion of the 3D object that is printed. The negative profile maybe analyzed (e.g., by the controller) to determine a cross-sectionalimage (i.e., a tomography, contour, or silhouette) of the at least theportion of the 3D object that has been printed. The determinedcross-sectional image of the at least the portion of the 3D object maybe compared to an initial 3D model of the 3D object to assess printquality. In some cases, the cross-sectional area and/or shape of a layerof the 3D object based on the negative image may be compared to atheoretical cross-sectional area and/or shape of a corresponding layerof the 3D object based on the initial 3D model of the 3D object, therebyto assess print quality.

A plurality of negative profiles of a plurality of portions of the 3Dobject may be combined (e.g., by the controller) to re-construct a 3Dmodel of at least a portion of the 3D object that is printed. Aplurality of cross-sectional images based on the plurality of negativeprofiles may be combined to generate the re-constructed 3D model of theat least the portion of the 3D object. Combining the plurality ofnegative profiles (or the respective plurality of cross-sectionalimages) may comprise stacking the plurality of negative profiles (or therespective plurality of cross-sectional images). The plurality ofportions of the 3D object may be sequential portions of the 3D object.The plurality of portions of the 3D object may not be sequentialportions of the 3D object. The virtual model of the at least the portionof the 3D object may be compared the initial 3D model of the 3D object,thereby to assess print quality. The virtual model may be as informativeas a reconstruction of the printed 3D object using micro-computedtomography.

The sensor(s) may be used prior to, during, and/or subsequent todepositing the film of viscous liquid on the build surface. Thesensor(s) may be used prior to, during, and/or subsequent to forming(e.g., curing, polymerizing, cross-linking, etc.) at least a portion ofthe film of viscous liquid into a polymer. The sensor(s) may be usedprior to, during, and/or subsequent to removing any excess viscousliquid from the build surface.

The method may comprise exposing the resin (e.g., the viscous liquid) tothe light (i.e., photoinitiation light) under conditions sufficient tocause the at least one photoinitiator to initiate formation of thepolymeric material from the polymeric precursor. The polymeric materialmay encapsulate the plurality of particles. The method may compriseexposing the resin to a different light (i.e., photoinhibition light)under conditions sufficient to cause the at least one photoinhibitor toinhibit formation of the polymeric material adjacent to the buildsurface. In some cases, the photoinitiation light may comprise a firstwavelength and the photoinhibition light may comprise a thirdwavelength. The first and third wavelengths may be different. The firstwavelength may be sufficient to activate the at least onephotoinitiator, and the third wavelength may be sufficient to activatethe at least one photoinhibitor.

The method may further comprise directing the light (i.e.,photoinitiation light) through the print window and to the film toinitiate formation (e.g., curing or cross-linking) of the polymericmaterial from the polymeric precursor. The light may be directed from anoptical source that provides the light through the print window and tothe film to initiate formation of the polymeric material from thepolymeric precursor. The optical source may provide the first lightthrough the print window (or above the print window) for forming the atleast a portion of the 3D object adjacent to the print window.

The method may further comprise directing the different light (i.e.,photoinhibition light) through the print window and to the film toinhibit formation (e.g., inhibit curing or cross-linking) of thepolymeric material from the polymeric precursor on or adjacent to theprint window. The different light may be directed from an optical sourcethat provides the different light through the print window and to thefilm to inhibit formation of the polymeric material from the polymericprecursor on or adjacent to the print window. The optical source mayprovide the different light through the print window (or above the printwindow) to inhibit formation of the polymeric material from thepolymeric precursor on or adjacent to the print window.

In some situations, the print window may be precluded. In such ascenario, light may be provided to the film of the viscous liquid fromabove the open platform, such as directly above or from a side of theopen platform.

Prior to providing the film comprising the polymeric precursor on oradjacent to the build surface, the method may comprise receiving orgenerating a computer model of the 3D object, wherein the at least theportion of the 3D object is in accordance to the computer model of the3D object. The method may further comprise determining an amount of theliquid (e.g., the viscous liquid) comprising the polymeric precursor tobe dispensed on or adjacent to the build surface for printing a portion(e.g., a layer) of the 3D object.

In some cases, the viscous liquid may be the photoactive resin. Theviscosity of the photoactive resin may range between about 4,000 cP toabout 2,000,000 cP. The viscosity of the photoactive resin may be atleast about 4,000 cP, 10,000 cP, 20,000 cP, 30,000 cP, 40,000 cP, 50,000cP, 60,000 cP, 70,000 cP, 80,000 cP, 90,000 cP, 100,000 cP, 200,000 cP,300,000 cP, 400,000 cP, 500,000 cP, 600,000 cP, 700,000 cP, 800,000 cP,900,000 cP, 1,000,000 cP, 2,000,000 cP, or more. The viscosity of thephotoactive resin may be at most about 2,000,000 cP, 1,000,000 cP,900,000 cP, 800,000 cP, 700,000 cP, 600,000 cP, 500,000 cP, 400,000 cP,300,000 cP, 200,000 cP, 100,000 cP, 90,000 cP, 80,000 cP, 70,000 cP,60,000 cP, 50,000 cP, 40,000 cP, 30,000 cP, 20,000 cP, 10,000 cP, 4,000cP, or less.

The viscous liquid may be a non-Newtonian fluid. The viscosity of theviscous liquid may vary based on a shear rate or shear history of theviscous liquid. As an alternative, the viscous liquid may be a Newtonianfluid.

In some cases, the viscous liquid may comprise the photoactive resin andthe plurality of particles. The viscosity of the viscous liquid mayrange between about 4,000 cP to about 2,000,000 cP. The viscosity of theviscous liquid may be at least about 4,000 cP, 10,000 cP, 20,000 cP,30,000 cP, 40,000 cP, 50,000 cP, 60,000 cP, 70,000 cP, 80,000 cP, 90,000cP, 100,000 cP, 200,000 cP, 300,000 cP, 400,000 cP, 500,000 cP, 600,000cP, 700,000 cP, 800,000 cP, 900,000 cP, 1,000,000 cP, 2,000,000 cP, ormore. The viscosity of the viscous liquid may be at most about 2,000,000cP, 1,000,000 cP, 900,000 cP, 800,000 cP, 700,000 cP, 600,000 cP,500,000 cP, 400,000 cP, 300,000 cP, 200,000 cP, 100,000 cP, 90,000 cP,80,000 cP, 70,000 cP, 60,000 cP, 50,000 cP, 40,000 cP, 30,000 cP, 20,000cP, 10,000 cP, 4,000 cP, or less.

In the viscous liquid comprising the photoactive resin and the pluralityof particles, the photoactive resin may be present in an amount rangingbetween about 5 volume % (vol %) to about 80 vol % in the viscousliquid. The photoactive resin may be present in an amount of at leastabout 5 vol %, 6 vol %, 7 vol %, 8 vol %, 9 vol %, 10 vol %, 11 vol %,12 vol %, 13 vol %, 14 vol %, 15 vol %, 16 vol %, 17 vol %, 18 vol %, 19vol %, 20 vol %, 21 vol %, 22 vol %, 23 vol %, 24 vol %, 25 vol %, 30vol %, 35 vol %, 40 vol %, 45 vol %, 50 vol %, 55 vol %, 60 vol %, 65vol %, 70 vol %, 75 vol %, 80 vol %, or more in the viscous liquid. Thephotoactive resin may be present in an amount of at most about 80 vol %,75 vol %, 70 vol %, 65 vol %, 60 ol %, 55 vol %, 50 vol %, 45 vol %, 40vol %, 35 vol %, 30 vol %, 25 vol %, 24 vol %, 23 vol %, 22 vol %, 21vol %, 20 vol %, 19 vol %, 18 vol %, 17 vol %, 16 vol %, 15 vol %, 14vol %, 13 vol %, 12 vol %, 11 vol %, 10 vol %, 9 vol %, 8 vol %, 7 vol%, 6 vol %, 5 vol %, or less in the viscous liquid.

The polymeric precursor in the photoactive resin may comprise monomersto be polymerized into the polymeric material, oligomers to becross-linked into the polymeric material, or both. The monomers may beof the same or different types. An oligomer may comprise two or moremonomers that are covalently linked to each other. The oligomer may beof any length, such as at least 2 (dimer), 3 (trimer), 4 (tetramer), 5(pentamer), 6 (hexamer), 7, 8, 9, 10, 20, 30, 40, 50, 100, 200, 300,400, 500, or more monomers. Alternatively or in addition to, thepolymeric precursor may include a dendritic precursor (monodisperse orpolydisperse). The dendritic precursor may be a first generation (G1),second generation (G2), third generation (G3), fourth generation (G4),or higher with functional groups remaining on the surface of thedendritic precursor. The resulting polymeric material may comprise amonopolymer and/or a copolymer. The copolymer may be a linear copolymeror a branched copolymer. The copolymer may be an alternating copolymer,periodic copolymer, statistical copolymer, random copolymer, and/orblock copolymer.

Examples of monomers include one or more of hydroxyethyl methacrylate;n-Lauryl acrylate; tetrahydrofurfuryl methacrylate; 2,2,2-trifluoroethylmethacrylate; isobornyl methacrylate; polypropylene glycolmonomethacrylates, aliphatic urethane acrylate (i.e., Rahn Genomer1122); hydroxyethyl acrylate; n-Lauryl methacrylate; tetrahydrofurfurylacrylate; 2,2,2-trifluoroethyl acrylate; isobornyl acrylate;polypropylene glycol monoacrylates; trimethylpropane triacrylate;trimethylpropane trimethacrylate; pentaerythritol tetraacrylate;pentaerythritol tetraacrylate; triethyleneglycol diacrylate; triethyleneglycol dimethacrylate; tetrathyleneglycol diacrylate; tetrathyleneglycol dimethacrylate; neopentyldimethacrylate; neopentylacrylate;hexane dioldimethacylate; hexane diol diacrylate; polyethylene glycol400 dimethacrylate; polyethylene glycol 400 diacrylate; diethylglycoldiacrylate; diethylene glycol dimethacrylate; ethyleneglycol diacrylate;ethylene glycol dimethacrylate; ethoxylated bis phenol A dimethacrylate;ethoxylated bis phenol A diacrylate; bisphenol A glycidyl methacrylate;bisphenol A glycidyl acrylate; ditrimethylolpropane tetraacrylate; andditrimethylolpropane tetraacrylate.

Polymeric precursors may be present in an amount ranging between about 3weight % (wt %) to about 90 wt % in the photoactive resin of the viscousliquid. The polymeric precursors may be present in an amount of at leastabout 3 wt %, 4 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt%, 35 wt %, 40 wt %, 45 wt %, 50 wt %, 55 wt %, 60 wt %, 65 wt %, 70 wt%, 75 wt %, 80 wt %, 85 wt %, 90 wt %, or more in the photoactive resinof the viscous liquid. The polymeric precursors may be present in anamount of at most about 90 wt %, 85 wt %, 80 wt %, 75 wt %, 70 wt %, 65wt %, 60 wt %, 55 wt %, 50 wt %, 45 wt %, 40 wt %, 35 wt %, 30 wt %, 25wt %, 20 wt %, 15 wt %, 10 wt %, 5 wt %, 4 wt %, 3 wt %, or less in thephotoactive resin of the viscous liquid.

Photopolymerization of the polymeric precursors into the polymericmaterial may be controlled by one or more photoactive species, such asthe at least one photoinitiator and the at least one photoinhibitor. Theat least one photoinitiator may be a photon-absorbing compound that (i)is activated by a light (i.e., photoinitiation light) comprising a firstwavelength and (ii) initiates photopolymerization of the polymericprecursors. The at least one photoinhibitor may be anotherphoton-absorbing compound that (i) is activated by a different light(i.e., photoinhibition light) comprising a third wavelength and (ii)inhibits the photopolymerization of the polymeric precursors. The firstwavelength and the third wavelength may be different. The light and thedifferent light may be directed by the same light source. As analternative, the light may be directed by a first light source (i.e.,photoinitiation light source) and the different light may be directed bya different light source (i.e., photoinhibition light source). In somecases, the light may comprise wavelengths ranging between about 420nanometers (nm) to about 510 nm. In some cases, the different light maycomprise wavelengths ranging between about 350 nm to about 410 nm. In anexample, the first wavelength to induce photoinitiation is about 460 nm.In an example, the third wavelength to induce photoinhibition is about365 nm.

Relative rates of the photoinitiation by the at least one photoinitiatorand the photoinhibition by the at least one photoinhibitor may becontrolled by adjusting the intensity and/or duration of the light, thedifferent light, or both. By controlling the relative rates of thephotoinitiation and the photoinhibition, an overall rate and/or amount(degree) of polymerization of the polymeric precursors into thepolymeric material may be controlled. Such process may be used to (i)prevent polymerization of the polymeric precursors at the window-viscousliquid interface, (ii) control the rate at which polymerization takesplace in the direction away from the window, and/or (iii) control athickness of the polymeric material within the film of the viscousliquid.

Examples of types of the at least one photoinitiator include one or moreof benzophenones, thioxanthones, anthraquinones, benzoylformate esters,hydroxyacetophenones, alkylaminoacetophenones, benzil ketals,dialkoxyacetophenones, benzoin ethers, phosphine oxides acyloximinoesters, alphahaloacetophenones, trichloromethyl-S-triazines,titanocenes, dibenzylidene ketones, ketocoumarins, dye sensitizedphotoinitiation systems, maleimides, and mixtures thereof.

Examples of the at least one photoinitiator in the photoactive resininclude one or more of 1-hydroxy-cyclohexyl-phenyl-ketone (Irgacure™184; BASF, Hawthorne, N.J.); a 1:1 mixture of1-hydroxy-cyclohexyl-phenyl-ketone and benzophenone (Irgacure™ 500;BASF); 2-hydroxy-2-methyl-1-phenyl-1-propanone (Darocur™ 1173; BASF);2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure™2959; BASF); methyl benzoylformate (Darocur™ MBF; BASF);oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester;oxy-phenyl-acetic 2-[2-hydroxy-ethoxy]-ethyl ester; a mixture ofoxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester andoxy-phenyl-acetic 2-[2-hydroxy-ethoxy]-ethyl ester (Irgacure™ 754;BASF); alpha,alpha-dimethoxy-alpha-phenylacetophenone (Irgacure™ 651;BASF);2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)-phenyl]-1-butanone(Irgacure™ 369; BASF);2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone(Irgacure™ 907; BASF); a 3:7 mixture of2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl) phenyl]-1-butanone andalpha,alpha-dimethoxy-alpha-phenylacetophenone per weight (Irgacure™1300; BASF); diphenyl-(2,4,6-trimethylbenzoyl) phosphine oxide (Darocur™TPO; BASF); a 1:1 mixture of diphenyl-(2,4,6-trimethylbenzoyl)-phosphineoxide and 2-hydroxy-2-methyl-1-phenyl-1-propanone (Darocur™ 4265; BASF);phenyl bis(2,4,6-trimethyl benzoyl) phosphine oxide, which can be usedin pure form (Irgacure™ 819; BASF, Hawthorne, N.J.) or dispersed inwater (45% active, Irgacure™ 819DW; BASF); 2:8 mixture of phosphineoxide, phenyl bis(2,4,6-trimethyl benzoyl) and2-hydroxy-2-methyl-1-phenyl-1-propanone (Irgacure™ 2022; BASF);Irgacure™ 2100, which comprisesphenyl-bis(2,4,6-trimethylbenzoyl)-phosphine oxide); bis-(eta5-2,4-cyclopentadien-1-yl)-bis-[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]-titanium (Irgacure™ 784; BASF); (4-methylphenyl)[4-(2-methylpropyl) phenyl]-iodonium hexafluorophosphate (Irgacure™ 250;BASF);2-(4-methylbenzyl)-2-(dimethylamino)-1-(4-morpholinophenyl)-butan-1-one(Irgacure™ 379; BASF);4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone (Irgacure™ 2959;BASF); bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide;a mixture of bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphineoxide and 2 hydroxy-2-methyl-1-phenyl-propanone (Irgacure™ 1700; BASF);4-Isopropyl-9-thioxanthenone; and mixtures thereof.

The at least one photoinitiator may be present in an amount rangingbetween about 0.1 wt % to about 10 wt % in the photoactive resin. The atleast one photoinitiator may be present in an amount of at least about0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %,0.8 wt %, 0.9 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt%, 8 wt %, 9 wt %, 10 wt %, or more in the photoactive resin. The atleast one photoinitiator may be present in an amount of at most about 10wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1wt %, 0.9 wt %, 0.8 wt %, 0.7 wt %, 0.6 wt %, 0.5 wt %, 0.4 wt %, 0.3 wt%, 0.2 wt %, 0.1 wt %, or less in the photoactive resin.

The at least one photoinhibitor in the photoactive resin may compriseone or more radicals that may preferentially terminate growing polymerradicals, rather than initiating polymerization of the polymericprecursors. Examples of types of the at least one photoinhibitorinclude: one or more of sulfanylthiocarbonyl and other radicalsgenerated in photoiniferter polymerizations; sulfanylthiocarbonylradicals used in reversible addition-fragmentation chain transferpolymerization; and nitrosyl radicals used in nitroxide mediatepolymerization. Other non-radical species that can be generated toterminate growing radical chains may include the numerous metal/ligandcomplexes used as deactivators in atom-transfer radical polymerization(ATRP). Thus, additional examples of the types of the at least onephotoinhibitor include: one or more of thiocarbamates, xanthates,dithiobenzoates, hexaarylbiimidazoles, photoinitiators that generateketyl and other radicals that tend to terminate growing polymer chainsradicals (i.e., camphorquinone (CQ) and benzophenones), ATRPdeactivators, and polymeric versions thereof.

Examples of the at least one photoinhibitors in the photoactive resininclude one or more of zinc dimethyl dithiocarbamate; zinc diethyldithiocarbamate; zinc dibutyl dithiocarbamate; nickel dibutyldithiocarbamate; zinc dibenzyl dithiocarbamate; tetramethylthiuramdisulfide; tetraethylthiuram disulfide (TEDS); tetramethylthiurammonosulfide; tetrabenzylthiuram disulfide; tetraisobutylthiuramdisulfide; dipentamethylene thiuram hexasulfide; N,N′-dimethylN,N′-di(4-pyridinyl)thiuram disulfide; 3-Butenyl2-(dodecylthiocarbonothioylthio)-2-methylpropionate;4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid;4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanol; Cyanomethyldodecyl trithiocarbonate; Cyanomethyl [3-(trimethoxysilyl)propyl]trithiocarbonate; 2-Cyano-2-propyl dodecyl trithiocarbonate;S,S-Dibenzyl trithiocarbonate;2-(Dodecylthiocarbonothioylthio)-2-methylpropionic acid;2-(Dodecylthiocarbonothi oylthio)-2-methylpropionic acidN-hydroxysuccinimide; Benzyl 1H-pyrrole-1-carbodithioate; Cyanomethyldiphenylcarbamodithioate; Cyanomethyl methyl(phenyl)carbamodithioate;Cyanomethyl methyl(4-pyridyl)carbamodithioate; 2-Cyanopropan-2-ylN-methyl-N-(pyridin-4-yl)carbamodithioate; Methyl2-[methyl(4-pyridinyl)carbamothioylthio]propionate;1-Succinimidyl-4-cyano-4-[N-methyl-N-(4-pyridyl)carbamothioylthio]pentanoate;Benzyl benzodithioate; Cyanomethyl benzodithioate;4-Cyano-4-(phenylcarbonothioylthio)pentanoic acid;4-Cyano-4-(phenylcarbonothioylthio)pentanoic acid N-succinimidyl ester;2-Cyano-2-propyl benzodithioate; 2-Cyano-2-propyl 4-cyanobenzodithioate;Ethyl 2-(4-methoxyphenylcarbonothioylthio)acetate; 2-Phenyl-2-propylbenzodithioate; Cyanomethyl methyl(4-pyridyl)carbamodithioate;2-Cyanopropan-2-yl N-methyl-N-(pyridin-4-yl)carbamodithioate;2,2′-Bis(2-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,2′-biimidazole;2-(2-ethoxyphenyl)-1-[2-(2-ethoxyphenyl)-4,5-diphenyl-2H-imidazol-2-yl]-4,5-diphenyl-1H-imidazole;2,2′,4-tris-(2-Chlorophenyl)-5-(3,4-dimethoxyphenyl)-4′,5′-diphenyl-1,1′-biimidazole;and Methyl 2-[methyl(4-pyridinyl)carbamothioylthio]propionate.

In some cases, the photoinhibitor may comprise a hexaarylbiimidazole(HABI) or a functional variant thereof. In some cases, thehexaarylbiimidazole may comprise a phenyl group with a halogen and/or analkoxy substitution. In an example, the phenyl group comprises anortho-chloro-substitution. In another example, the phenyl groupcomprises an ortho-methoxy-substitution. In another example, the phenylgroup comprises an ortho-ethoxy-substitution. Examples of the functionalvariants of the hexaarylbiimidazole include:2,2′-Bis(2-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,2′-biimidazole;2-(2-methoxyphenyl)-1-[2-(2-methoxyphenyl)-4,5-diphenyl-2H-imidazol-2-yl]-4,5-diphenyl-1H-imidazole;2-(2-ethoxyphenyl)-1-[2-(2-ethoxyphenyl)-4,5-diphenyl-2H-imidazol-2-yl]-4,5-diphenyl-1H-imidazole;and2,2′,4-tris-(2-Chlorophenyl)-5-(3,4-dimethoxyphenyl)-4′,5′-diphenyl-1,1′-biimidazole.

The at least one photoinhibitor may be present in an amount rangingbetween about 0.1 wt % to about 10 wt % in the photoactive resin. The atleast one photoinhibitor may be present in an amount of at least about0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %,0.8 wt %, 0.9 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt%, 7 wt %, 8 wt %, 9 wt %, 10 wt %, or more in the photoactive resin.The at least one photoinhibitor may be present in an amount of at mostabout 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, 3 wt %, 2wt %, 1 wt %, 0.9 wt %, 0.8 wt %, 0.7 wt %, 0.6 wt %, 0.5 wt %, 0.4 wt%, 0.3 wt %, 0.2 wt %, 0.1 wt %, or less in the photoactive resin.

Alternatively or in addition to, the photoactive resin may include aco-initiator. The co-initiator may be used to enhance the polymerizationrate of the polymeric precursors. Suitable classes of the co-initiatorsmay include: primary, secondary, and tertiary amines; alcohols; andthiols. Examples of the co-initiators may include: one or more ofisoamyl 4-(dimethylamino)benzoate, 2-ethylhexyl4-(dimethylamino)benzoate; ethyl 4-(dimethylamino)benzoate (EDMAB);3-(dimethylamino)propyl acrylate; 2-(dimethylamino)ethyl methacrylate;4-(dimethylamino)benzophenones, 4-(diethylamino)benzophenones;4,4′-Bis(diethylamino)benzophenones; methyl diethanolamine;triethylamine; hexane thiol; heptane thiol; octane thiol; nonane thiol;decane thiol; undecane thiol; dodecane thiol; isooctyl3-mercaptopropionate; pentaerythritol tetrakis(3-mercaptopropionate);4,4′-thiobisbenzenethiol; trimethylolpropane tris(3-mercaptopropionate);CN374 (Sartomer); CN371 (Sartomer), CN373 (Sartomer), Genomer 5142(Rahn); Genomer 5161 (Rahn); Genomer (5271 (Rahn); Genomer 5275 (Rahn),and TEMPIC (Bruno Boc, Germany).

In some cases, the at least one photoinitiator and the co-initiator maybe activated by the same light. The at least one photoinitiator and theco-initiator may be activated by the same wavelength and/or twodifferent wavelengths of the same light. Alternatively or in additionto, the at last one photoinitiator and the co-initiator may be activatedby different lights comprising different wavelengths. The method maycomprise providing a co-initiator light source configured to direct aco-initiation light comprising a wavelength sufficient to activate theco-initiator to the film of the viscous liquid.

The co-initiator may be a small molecule (e.g., a monomer).Alternatively or in addition to, the co-initiator may be an oligomer orpolymer comprising a plurality of small molecules. The co-initiator maybe present in an amount ranging between about 0.1 wt % to about 10 wt %in the photoactive resin. The co-initiator may be present in an amountof at least about 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt%, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, or more in the photoactiveresin. The co-initiator may be present in an amount of at most about 10wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1wt %, 0.9 wt %, 0.8 wt %, 0.7 wt %, 0.6 wt %, 0.5 wt %, 0.4 wt %, 0.3 wt%, 0.2 wt %, 0.1 wt %, or less in the photoactive resin.

The photoactive resin may comprise one or more dyes. The one or moredyes may be used to attenuate light, to transfer energy to thephotoactive species, or both. The one or more dyes may transfer energyto the photoactive species to increase sensitivity of the photoactiveresin to the light for the photoinitiation process, the different lightfor the photoinhibition process, or both. In an example, the photoactiveresin comprises at least one dye configured to absorb the differentlight having the third wavelength, which third wavelength is foractivating the at least one photoinhibitor. Exposing the photoactiveresin to the different light may initiate the at least one dye to absorbthe different light and (i) reduce an amount of the different lightexposed to the at least one photoinhibitor, thereby controlling thedepth of penetration of the different light into the film of the viscousliquid, and/or (ii) transfer (e.g., via Förster resonance energytransfer (FRET)) some of the absorbed energy from the different light tothe at least one photoinhibitor, thereby improving the efficiency ofphotoinhibition. Examples of the one or more dyes may include compoundscommonly used as ultraviolet (UV) light absorbers, including2-hydroxyphenyl-benzophenones, 2-(2-hydroxyphenyl)-benzotriazoles, and2-hydroxyphenyl-s-triazines. Alternatively or in addition to, the one ormore dyes may include those used for histological staining or dying offabrics, including Martius yellow, Quinoline yellow, Sudan red, Sudan I,Sudan IV, eosin, eosin Y, neutral red, and acid red.

A concentration of the one or more dyes in the photoactive resin may bedependent on the light absorption properties of the one or more dyes.The one or more dyes may be present in an amount ranging between about0.1 wt % to about 10 wt % in the photoactive resin. The one or more dyesmay be present in an amount of at least about 0.1 wt %, 0.2 wt %, 0.3 wt%, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1 wt %, 2wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %,or more in the photoactive resin. The one or more dyes may be present inan amount of at most about 10 wt %, 9 wt %, 8 wt %, 7 wt %, 6 wt %, 5 wt%, 4 wt %, 3 wt %, 2 wt %, 1 wt %, 0.9 wt %, 0.8 wt %, 0.7 wt %, 0.6 wt%, 0.5 wt %, 0.4 wt %, 0.3 wt %, 0.2 wt %, 0.1 wt %, or less in thephotoactive resin.

The viscous liquid may comprise the plurality of particles for formingthe at least the portion of the 3D object. In some cases, the amount ofthe plurality of particles in the viscous liquid may be sufficient tominimize shrinking of the green body during sintering. The plurality ofparticles may comprise any particulate material (a particle) that can bemelted or sintered (e.g., not completely melted). The particulatematerial may be in powder form. The particular material may be inorganicmaterials. The inorganic materials may be metallic, intermetallic,ceramic materials, or any combination thereof. The one or more particlesmay comprise at least one metallic material, at least one intermetallicmaterial, at least one ceramic material, or any combination thereof.

Whereas powdered metals alone may be a severe safety hazard and mayexplode and/or require extensive safety infrastructures, using powderedmetals that are dispersed in the viscous liquid may avoid orsubstantially reduce the risks relevant to using the powdered metalsthat are not dispersed in a liquid medium. Additionally,photopolymer-based 3D printing using the viscous liquid comprising thephotoactive resin and the powdered metals may be performed without usingheat, thereby avoiding or substantially reducing thermal distortion tothe at least the portion of the 3D object during printing.

The metallic materials for the particles may include one or more ofaluminum, calcium, magnesium, barium, scandium, titanium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium,niobium, molybdenum, ruthenium, rhodium, silver, cadmium, actinium, andgold. In some cases, the particles may comprise a rare earth element.The rare earth element may include one or more of scandium, yttrium, andelements of the lanthanide series having atomic numbers from 57-71.

An intermetallic material may be a solid-state compound exhibitingmetallic bonding, defined stoichiometry and ordered crystal structure(i.e., alloys). The intermetallic materials may be in prealloyed powderform. Examples of such prealloyed powders may include, but are notlimited to, brass (copper and zinc), bronze (copper and tin), duralumin(aluminum, copper, manganese, and/or magnesium), gold alloys (gold andcopper), rose-gold alloys (gold, copper, and zinc), nichrome (nickel andchromium), and stainless steel (iron, carbon, and additional elementsincluding manganese, nickel, chromium, molybdenum, boron, titanium,silicon, vanadium, tungsten, cobalt, and/or niobium). In some cases, theprealloyed powders may include superalloys. The superalloys may be basedon elements including iron, nickel, cobalt, chromium, tungsten,molybdenum, tantalum, niobium, titanium, and/or aluminum.

The ceramic materials may comprise metal (e.g., aluminum, titanium,etc.), non-metal (e.g., oxygen, nitrogen, etc.), and/or metalloid (e.g.,germanium, silicon, etc.) atoms primarily held in ionic and covalentbonds. Examples of the ceramic materials include, but are not limitedto, an aluminide, boride, beryllia, carbide, chromium oxide, hydroxide,sulfide, nitride, mullite, kyanite, ferrite, titania zirconia, yttria,and magnesia.

In some cases, the viscous liquid may comprise a pre-ceramic material.The pre-ceramic material may be a polymer that can be heated (orpyrolyzed) to form a ceramic material. The pre-ceramic material mayinclude polyorganozirconates, polyorganoaluminates, polysiloxanes,polysilanes, polysilazanes, polycarbosilanes, polyborosilanes, etc.Additional examples of the pre-ceramic material include zirconiumtetramethacrylate, zirconyl dimethacrylate, or zirconium2-ethylhexanoate; aluminum III s-butoxide, aluminum IIIdiisopropoxide-ethylacetoacetate; 1,3-bis(chloromethyl)1,1,3,3-Tetrakis(trimethylsiloxy)disiloxane;1,3-bis(3-carboxypropyl)tetramethyldisiloxane;1,3,5,7-tetraethyl-2,4,6,8-tetramethylcyclotetrasilazane;tris(trimethylsilyl)phosphate; tris(trimethylsiloxy)boron; and mixturesthereof.

A cross-sectional dimension of the plurality of particles may rangebetween about 1 nanometers (nm) to about 500 micrometers (μm). Thecross-sectional dimension of the plurality of particles may be at leastabout 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 20nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, orgreater. The cross-sectional dimension of the plurality of particles maybe at most about 500 μm, 400 μm, 300 μm, 200 μm, 100 μm, 90 μm, 80 μm,70 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20 μm, 10 μm, 9 μm, 8 μm, 7 μm, 6 μm,5 μm, 4 μm, 3 μm, 2 μm, 1 μm, 900 nm, 800 nm, 700 nm, 600 nm, 500 nm,400 nm, 300 nm, 200 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40nm, 30 nm, 20 nm, 10 nm, 9 nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3 nm, 2 nm,1 nm, or smaller.

The plurality of particles (e.g., metallic, intermetallic, and/orceramic particles) may be present in an amount ranging between about 5vol % to about 90 vol % in the viscous liquid. The plurality ofparticles may be present in an amount of at least about 5 vol %, 10 vol%, 15 vol %, 20 vol %, 25 vol %, 30 vol %, 35 vol %, 40 vol %, 45 vol %,50 vol %, 55 vol %, 60 vol %, 65 vol %, 70 vol %, 75 vol %, 80 vol %, 85vol %, 90 vol %, or more in the viscous liquid. The plurality ofparticles may be present in an amount of at most about 90 vol %, 85 vol%, 80 vol %, 75 vol %, 70 vol %, 65 vol %, 60 vol %, 55 vol %, 50 vol %,45 vol %, 40 vol %, 35 vol %, 30 vol %, 25 vol %, 20 vol %, 15 vol %, 10vol %, 5 vol %, or less in the viscous liquid.

The viscous liquid may comprise an anti-settling component to preventsettling of the plurality of particles and keep them suspend in theviscous liquid. The anti-settling component may sterically limit theplurality of particles from moving closer to each other. Theanti-settling component may not scatter light (e.g., the photoinitiationlight and/or the photoinhibition light) to avoid negatively affectingthe penetration depth of the light into the viscous liquid. Theanti-settling component may be present in an amount ranging betweenabout 5 vol % to about 90 vol % in the viscous liquid. The anti-settlingcomponent may be present in an amount of at least about 5 vol %, 10 vol%, 15 vol %, 20 vol %, 25 vol %, 30 vol %, 35 vol %, 40 vol %, 45 vol %,50 vol %, 55 vol %, 60 vol %, 65 vol %, 70 vol %, 75 vol %, 80 vol %, 85vol %, 90 vol %, or more in the viscous liquid. The anti-settlingcomponent may be present in an amount of at most about 90 vol %, 85 vol%, 80 vol %, 75 vol %, 70 vol %, 65 vol %, 60 vol %, 55 vol %, 50 vol %,45 vol %, 40 vol %, 35 vol %, 30 vol %, 25 vol %, 20 vol %, or less inthe viscous liquid. In some cases, the plurality of particles arepresent in an amount below the critical volume fraction (V_(C)) in theviscous liquid, and the anti-settling component may be added toapproximately reach the critical volume fraction (V_(C)) in the viscousliquid.

Examples of the anti-settling component include, but are not limited to,one or more additional particles and a thixotropic additive. The one ormore additional particles may be configured to prevent settling of theplurality of particles in the viscous liquid. The one or more additionalparticles may decrease free space and increase the overall packingdensity within the viscous liquid, thereby preventing the plurality ofparticles from settling towards the window during printing. Examples ofthe one or more additional particles include micronized and/or dispersedwaxes such as paraffin, carnuba, montan, Fischer tropsch wax, ethylenebis stearamide, and lignin; micronized polymers such as cellulose, highdensity polyethylene, polyethylene, polypropylene, oxidized polyethylene(PE), paraformaldehyde, polyethylene glycol, phenolics, andmelamine-formaldehyde based materials; and microspheres made fromcrosslinked polystyrene, polymethyl methacrylate, and/or othercopolymers. An example of the one or more additional particles is BykCeraflour 929 (micronized, modified polyethylene wax).

The thixotropic additive may be a gel-like or static material thatbecomes fluid-like when physically disturbed. Such property may bereversible. In the viscous liquid, the thixotropic additive may beconfigured to create a network to prevent settling of the plurality ofparticles. The network of the thixotropic additive may be easilydisturbed by shearing (e.g., dispensing through the nozzle) the viscousliquid to allow flow. Upon being dispensed through the nozzle, thethixotropic additive may form another network within the viscous liquidto prevent settling of the plurality of particles during printing.Examples of the thixotropic additive include castor wax, oxidizedpolyethylene wax, amide wax, modified ureas, castor oil derivatives,fumed silica and alumina, Bentonite clays, and mixtures thereof.

In some cases, the anti-settling component of the viscous liquid may bethe one or more additional particles, the thixotropic additive, or both.

The viscous liquid may comprise at least one additional additive that isconfigured to prevent foaming (or induce deaeration) of the viscousliquid. Preventing foaming of the viscous liquid may improve quality ofthe resulting 3D object. The at least one additional additive may be anamphiphilic material. The at least one additional additive may be a lowsurface energy material to allow association with each other within theviscous liquid. Such association of the at least one additional additivemay trap air bubbles present inside the viscous liquid, migrate towardsthe viscous liquid-air interface, and release the air bubbles. In somecases, during curing of the photoactive resin, the at least oneadditional additive may polymerize and/or cross-link with the polymericprecursor. Examples of the one additional additive include silcones,modified silicones, lauryl acrylates, hydrophobic silicas, and modifiedureas. An example of the one additional additive may be Evonik Tegorad2500 (silicon acrylate).

The viscous liquid may comprise an extractable material. Accordingly,the method may comprise additional operations of treating the green bodyprior to subjecting the green body to heating (e.g., sintering).

The extractable material may be soluble in the polymeric precursorand/or dispersed throughout the viscous liquid. During printing, curingof the polymeric precursor of the photoactive resin of the at least theportion of the viscous liquid may create a first solid phase comprisingthe polymeric material and a second solid phase comprising theextractable material within the at least the portion of the 3D object.Such process may be a polymerization-induced phase separation (PIPS)operation. At least a portion of the plurality of particles may beencapsulated by the first solid phase comprising the polymeric material.In some cases, the at least the portion of the 3D object may be a greenbody that can be heated to sinter at least a portion of the plurality ofparticles and burn off at least a portion of other components (i.e.,organic components).

Prior to sintering the plurality of particles, the green body may betreated (e.g., immersed, jetted, etc.) with a solvent (liquid or vapor).The solvent may be an extraction solvent. The extractable material maybe soluble in the solvent. A first solubility of the extractablematerial in the solvent may be higher than a second solubility of thepolymeric material in the solvent. The solvent may be a poor solvent forthe polymeric material. Thus, treating the green body with the solventmay solubilize and extract at least a portion of the extractablematerial out of the green body into the solvent, and create one or morepores in the at least the portion of the 3D object. In some cases, theone or more pores may be a plurality of pores. In some cases, the greenbody may be treated with the solvent and heat at the same time. The oneor more pores may create at least one continuous porous network in theat least the portion of the 3D object. Such process may be a solventde-binding operation.

The solvent for the solvent de-binding process may not significantlyswell the polymeric material in the green body. In some cases, theviscous liquid may comprise acrylate-based polymeric precursors. Sinceacrylate-based polymers are of intermediate polarity, both protic polarsolvents (e.g., water and many alcohols such as isopropanol) andnon-polar solvents (e.g., heptane) may be used. Examples of the solventfor the solvent de-binding process include water, isopropanol, heptane,limolene, toluene, and palm oil. On the other hand, intermediatepolarity solvents (e.g., acetone) may be avoided.

In some cases, the solvent de-binding process may involve immersing thegreen body in a container comprising the liquid solvent. A volume of thesolvent may be at least about 2 times the volume of the green body. Thevolume of the solvent may be at least about 2, 3, 4, 5, 6, 7, 8, 9, 10times or more than the volume of the green body. The containercomprising the liquid solvent and the green body may be heated to atemperature ranging between about 25 degrees Celsius to about 50 degreesCelsius. The container comprising the liquid solvent and the green bodymay be heated (e.g., a water bath, oven, or a heating unit from one ormore sides of the green body) to a temperature of at least about 25degrees Celsius, 26 degrees Celsius, 27 degrees Celsius, 28 degreesCelsius, 29 degrees Celsius, 30 degrees Celsius, 35 degrees Celsius, 40degrees Celsius, 45 degrees Celsius, 50 degrees Celsius, or more. Thecontainer comprising the liquid solvent and the green body may be heatedto a temperature of at most about 50 degrees Celsius, 45 degreesCelsius, 40 degrees Celsius, 35 degrees Celsius, 30 degrees Celsius, 29degrees Celsius, 28 degrees Celsius, 27 degrees Celsius, 26 degreesCelsius, 25 degrees Celsius, or less. The solvent de-binding process maylast between about 0.1 hours (h) to about 48 h. The solvent de-bindingprocess may last between at least about 0.1 h, 0.2 h, 0.3 h, 0.4 h, 0.5h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 12 h, 18 h, 24 h, 30 h, 36 h, 42 h, 48h, or more. The solvent de-binding may last between at most about 48 h,42 h, 36 h, 30 h, 24 h, 18 h, 12 h, 6 h, 5 h, 4 h, 3 h, 2 h, 1 h, 0.5 h,0.4 h, 0.3 h, 0.2 h, 0.1 h, or less. After the solvent de-bindingprocess, the solvent may be removed and the green body may be allowed todry. A weight of the green body may be measured before and after thesolvent de-binding to determine the amount of material extracted fromthe green body.

After the solvent de-binding process, the green body may be heated(e.g., sintered) and/or cooled as abovementioned. During heating (e.g.,sintering), at least a portion of the organic components (e.g., thepolymeric material, additives, etc.) may decompose and leave the greenbody in part through the at least one continuous porous network. Thepresence of the at least one continuous porous network from the solventde-binding operation may improve the speed of the sintering process.

Subsequent to heating the green body, the heated (e.g., sintered)particles as part of a nascent 3D object may be further processed toyield the 3D object. This may include, for example, performing surfacetreatment, such as polishing, on the nascent 3D object.

The method may further comprise providing a deposition head adjacent toan open platform comprising a print window. The deposition head may bemovable across the open platform. The deposition head may comprise anozzle in fluid communication with a source of a viscous liquidcomprising a photoactive resin. The deposition head may comprise awiper. The method may comprise moving the deposition head across theopen platform and dispensing the viscous liquid through the nozzle todeposit a film of the viscous liquid over the print window. The methodmay comprise directing light through the print window to the film tocure the photoactive resin in at least a portion of the film, therebyprinting at least a portion of the 3D object.

The method may further comprise providing at least one deposition head(e.g., at least about 1, 2, 3, 4, 5, or more deposition heads, or atmost about 5, 4, 3, 2, or 1 deposition head) adjacent to the buildsurface and moving the deposition head across the build surface todeposit the film adjacent to the build surface. The deposition head maycomprise at least one nozzle (e.g., at least about 1, 2, 3, 4, 5, ormore nozzles, or at most about 5, 4, 3, 2, or 1 nozzle) in fluidcommunication with a source of the viscous liquid.

The deposition head may be configured to move across the open platformand deposit the film of the viscus liquid over the print window. Thefilm of the viscous liquid may have a thickness ranging between about 1μm to about 1000 μm. The film of the viscous liquid may have a thicknessof at least about 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm,10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 100 μm, 200 μm,300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, ormore. The film of the viscous liquid may have a thickness of at mostabout 1000 μm, 900 μm, 800 μm, 700 μm, 600 μm, 500 μm, 400 μm, 300 μm,200 μm, 100 μm, 90 μm, 80 μm, 70 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20 μm,10 μm, 9 μm, 8 μm, 7 μm, 6 μm, 5 μm, 4 μm, 3 μm, 2 μm, 1 μm, or less.The thickness of the film of the viscous liquid may have a toleranceranging between about 1 μm to about 10 μm. The thickness of the film ofthe viscous liquid may have a tolerance of at least about 1 μm, 2 μm, 3μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or more. The thickness ofthe film of the viscous liquid may have a tolerance of at most about 10μm, 9 μm, 8 μm, 7 μm, 6 μm, 5 μm, 4 μm, 3 μm, 2 μm, 1 μm, or less.

The viscous liquid may be stored in the source of the viscous liquid.The source of the viscous liquid may be a cup, container, syringe, orany other repository that can hold the viscous liquid. The source of theviscous liquid may be in fluid communication (e.g., via a passageway)with the nozzle in the deposition head. The source of the viscous liquidmay be connected to a flow unit. The flow unit may provide and controlflow of the viscous liquid from the source of the viscous liquid towardsthe nozzle, thereby dispensing the viscous liquid. Alternatively or inaddition to, the flow unit may provide and control flow of the viscousliquid in a direction away from the nozzle and towards the source of theviscous liquid, thereby retrieving the viscous liquid. In some cases,the flow unit may use pressure mechanisms to control the speed anddirection of the flow of the viscous liquid. The flow unit may be asyringe pump, vacuum pump, an actuator (e.g., linear, pneumatic,hydraulic, etc.), a compressor, or any other suitable device to exertpressure (positive or negative) to the viscous liquid in the source ofthe viscous liquid. The controller may be operatively coupled to theflow unit the control the speed, duration, and/or direction of the flowof the viscous liquid.

The source of the viscous liquid may comprise a sensor (e.g., an opticalsensor) to detect the volume of the viscous liquid. The controller maybe operatively coupled to the sensor to determine when the source of theviscous liquid may be replenished with new viscous liquid. Alternativelyor in addition to, the source of the viscous liquid may be removable.The controller may determine when the source of the viscous liquid maybe replaced with a new source of the viscous liquid comprising with theviscous liquid.

The deposition head may comprise the nozzle. The nozzle may be in fluidcommunication with the source of the viscous liquid. The deposition headmay dispense the viscous liquid over the print window through the nozzleas a process of depositing the film of the viscous liquid over the printwindow. In some cases, the deposition head may retrieve any excessviscous liquid from the print window back into the source of the viscousliquid through the nozzle. In some cases, the source of the viscousliquid may be connected to the flow unit to provide and control flow ofthe viscous liquid towards or away from the nozzle of the depositionhead. Alternatively or in addition to, the nozzle may comprise a nozzleflow unit that provides and controls flow of the viscous liquid towardsor away from the print window. Examples of the nozzle flow unit includea piezoelectric actuator and an auger screw that is connected to anactuator.

In some cases, the method may further comprise configuring the wiper tobe in contact with the print window, and using the wiper to reduce orinhibit flow of the viscous liquid out of the deposition head whilemoving the deposition head to deposit the film.

In some cases, the method may further comprise configuring the wiper ata distance away from the print window, and using the wiper to flattenthe film of the viscous liquid into a desired thickness while moving thedeposition head. The desired thickness of the film of the viscous liquidmay be substantially the same as the distance between the wiper and theprint window. The distance between the wiper and the print window may beadjustable. Thus, the thickness of the film of the viscous liquid may beadjustable. The thickness of the film may be adjusted to control athickness of the at least the portion of the 3D object. In some cases,after printing the at least the portion of the 3D object, the method mayfurther comprise moving the deposition head across the open platform ina first direction, and using the wiper of the deposition head that is incontact with the print window to remove any excess of the viscous liquidfrom the print window. Furthermore, in some cases, the deposition headmay further comprise an additional wiper. After moving the depositionhead in the first direction and using the wiper to remove the excess ofthe viscous liquid from the print window, the method may furthercomprise moving the deposition head in the second direction opposite ofthe first direction and using the additional wiper to collect the excessof the viscous liquid between the additional wiper and the wiper withinthe deposition head.

The deposition head may comprise a wiper. The wiper may be movable alonga direction towards and/or away from the print window. The wiper mayhave a variable height relative to the print window. The deposition headmay comprise an actuator connected to the wiper to control movement ofthe wiper in a direction towards and away from the print window. Theactuator may be a mechanical, hydraulic, pneumatic, orelectro-mechanical actuator. The controller may be operatively coupledto the actuator to control the movement of the wiper in a directiontowards and away from the print window. Alternatively or in addition to,a vertical distance between the wiper and the print window (e.g., adistance perpendicular to the print window) may be static. In somecases, the deposition head may comprise a plurality of wipers withdifferent configurations. In some cases, the deposition head maycomprise the nozzle and three wipers.

The wiper of the deposition head may be configured to (i) reduce orinhibit flow of the viscous liquid out of the deposition head, (ii)flatten the film of the viscous liquid, and/or (iii) remove any excessof the viscous liquid. In an example, the wiper may be configured to bein contact with the print window and reduce or inhibit flow of theviscous liquid out of the deposition head. In another example, the wipermay be movable along a direction away from the print window andconfigured to flatten the film of the viscous liquid. The wiper mayflatten the film of the viscous liquid to a defined height (orthickness). In a different example, the wiper may be movable along adirection away from the print window and configured to remove the excessof the viscous liquid.

The wiper may comprise polymer (e.g., rubber, silicone), metal, orceramic. In some cases, the wiper may comprise (e.g., entirely or as acoating) one or more fluoropolymers that prevent adhesion of the viscousliquid on the wiper. Examples of the one or more fluoropolymers includepolyvinylidene fluoride (PVDF), ethylenchlorotrifluoroethylene (ECTFE),ethylenetetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE),perfluoroalkoxy (PFA), and modified fluoroalkoxy (a copolymer oftetrafluoroethylene and perfluoromethylvinylether, also known as MFA).

In some cases, the wiper of the deposition head may be a blade (e.g., asqueegee blade, a doctor blade). The blade may have various shapes. Insome cases, the blade may be straight and/or curved. In some cases, thewiper may be a straight blade with a flat surface. In some cases, thewiper may be a straight blade with a curved surface. In some cases, thewiper may be a curved blade (curved along the long axis of the wiper)with a flat surface. In some cases, the wiper may be a curved blade(curved along the long axis of the wiper) with a curved surface. In somecases, the wiper may comprise at least one straight portion and at leastone curved portion along its length. In an example, the wiper may be ablade comprising a straight central portion between two curved portions.

In some cases, the wiper of the deposition head may be a roller. Theroller may have a surface that is flat or textured. The roller may beconfigured to rotate clockwise and/or counterclockwise while thedeposition head moves across the print window. Alternatively or inaddition to, the roller may be configured to be static while thedeposition head moves across the print window. In some cases, the wiperof the deposition head may be a rod. The rod may have a surface that isflat or textured. The rod may be configured to rotate clockwise and/orcounterclockwise while the deposition head moves across the printwindow. Alternatively or in addition to, the rod may be configured to bestatic while the deposition head moves across the print window. In anexample, the rod may be a wire wound rod, also known as a Meyer rod.

The deposition head may comprise a slot die. The slot die may beconfigured to move along a direction away from the print window. Theslot die may be height adjustable with respect to the print window. Theslot die may comprise a channel in fluid communication with the sourceof the viscous liquid. The channel may comprise a first opening toreceive the viscous liquid from the source of the viscous liquid. Thechannel may comprise a second opening opposite of the first opening todispense the viscous liquid to the print window. The second opening maybe an injection point. In some cases, the channel may have a reservoirbetween the first and second openings to hold a volume of the viscousliquid. The injection point of the slot die may comprise a flat surfaceto flatten the film of the viscous liquid to a defined height (orthickness).

The deposition head comprising the slot die may include a separatenozzle to suction and retrieve any excess viscous liquid from the filmof the viscous liquid during printing. The separate nozzle of thedeposition head comprising the slot die may be in fluid communicationwith a repository to collect the excess viscous liquid. The repositorymay be a recycling bin. The repository may also be in fluidcommunication with the slot die to send the excess viscous liquidcollected in the repository back into the reservoir of the slot die.Alternatively or in addition to, the collected excess viscous liquid maybe removed for reprocessing. The reprocessing of the collected excessviscous liquid may comprise (i) filtering out any polymerized solidparticulates, (ii) filtering out any of the plurality of particles thatmay be greater than a target particle size, (iii) remixing the viscousliquid to ensure homogeneity, and/or (iv) removing at least a portion ofair entrapped in the viscous liquid. In some cases, the at least theportion of air entrapped in the viscous liquid may be removed bycentrifuging the viscous liquid.

The excess of the viscous liquid may be collected and used (recycled) todeposit an additional film of the viscous liquid over the print window.In some cases, if a volume of the excess of viscous liquid collected bythe deposition head is not sufficient to deposit the additional film,the nozzle of the deposition head may dispense more viscous liquid intothe collected excess of viscous liquid. In an example, the controllermay use a computer model of the 3D object, such as a computer-aideddesign (CAD) stored in a non-transitory computer storage medium, todetermine theoretical amounts of (i) the viscous liquid used in a firstprinting operation and (ii) the excess of the viscous liquid remainingon the print window. The controller may also use the computer model ofthe 3D object to determine a theoretical amount of the viscous liquidneeded to deposit a film of the viscous liquid for the second printingoperation. If the volume of the collected excess of viscous liquid isnot sufficient for the second printing operation, the controller maydirect the nozzle to dispense more viscous liquid. In some cases, thesystem may comprise a repository (e.g., vat or container) adjacent tothe open platform. After each printing operation, the deposition headmay move to the repository and collect the excess viscous liquid intothe repository. The collected excess viscous liquid may be reprocessedand used for printing.

The deposition head may be coupled to a motion stage adjacent to theopen platform. Thus, the method may comprise moving the motion stage tomove the deposition head across the open platform to at least depositthe film of the viscous liquid on the print window. The open platformmay have different shapes (e.g., rectangle or ring), and movement of themotion stage may have different paths. In some cases, the motion stagemay move linearly, thereby directing the deposition head in a firstdirection and/or in a second direction that is opposite to the firstdirection. In some cases, the motion stage may move circularly, therebydirection the deposition clockwise and/or counterclockwise.

The method may comprise using a plurality of viscous liquids forprinting the 3D objet. In some cases, the method may comprise providingan additional deposition head comprising an additional nozzle. Theadditional nozzle may be in fluid communication with an additionalsource of an additional viscous liquid. The method may further comprisemoving the additional deposition head across the open platform anddepositing a film of the additional viscous liquid over the printwindow. In some cases, the method may comprise providing the additionalsource of the additional viscous liquid that is in fluid communicationwith the nozzle of the deposition head. The method may further comprisedispensing the additional viscous liquid through the nozzle to the printwindow during printing. Alternatively or in addition to, the method maycomprise providing the additional source of the additional viscousliquid that is in fluid communication with an additional nozzle in thedeposition head. The method may further comprise dispensing theadditional viscous liquid through the additional nozzle to the printwindow during printing.

The additional nozzle of the additional deposition head may be in fluidcommunication with an additional source of an additional viscous liquid.In some cases, the nozzle of the deposition head may be in fluidcommunication with the source of the viscous liquid and the additionalsource of the additional viscous liquid. Alternatively or in additionto, the deposition head may comprise a first nozzle in fluidcommunication with the source of the viscous liquid, and (b) a secondnozzle in fluid communication with the additional source of theadditional viscous liquid. The presence of the additional source of theadditional viscous liquid may allow printing at least a portion of a 3Dobject comprising multiple materials (multi-materials) in differentlayers and/or in different portions within the same layer.

The viscous liquid and the additional viscous liquid may be the same. Asan alternative, the viscous liquid and the additional viscous liquid maybe different. The viscous liquid and the additional viscous liquid maycomprise different types of the photoactive resin, the plurality ofparticles, or both. Alternatively or in addition to, the viscous liquidand the additional viscous liquid may comprise different amounts(concentrations by weight or volume) of the photoactive resin, theplurality of particles, or both. In an example, the viscous liquid maycomprise metallic particles, and the additional viscous liquid maycomprise ceramic particles. A first concentration of the metallicparticles in the viscous liquid and a second concentration of theceramic particles in the additional viscous liquid may be the same ordifferent. A first photoactive resin in the viscous liquid and a secondphotoactive resin in the additional viscous liquid may be the same ordifferent. In another example, the viscous liquid may comprise a firsttype of metallic particles, and the additional viscous liquid maycomprise a second type of metallic particles. In a different example,the viscous liquid may comprise ceramic particles at a firstconcentration, and the additional viscous liquid may comprise the sameceramic particles at a second concentration that is different from thefirst concentration.

The method may comprise providing a cleaning zone. The cleaning zone maybe configured adjacent to the open platform. The method may furthercomprise moving the deposition head to the cleaning zone and activatingthe cleaning zone to clean the deposition head. The deposition head maybe cleaned prior to depositing a new film of the viscous liquid. Thedeposition head may be cleaned subsequent to printing at least a portionof the 3D object. The cleaning zone may be configured in a path ofmovement of the deposition head across the open platform. The cleaningzone may be configured to clean the deposition head. Cleaning thedeposition head may (i) improve reliability and reproducibility ofprinting at least the portion of the 3D object, and (ii) reduce wear andtear of the deposition head. The deposition head may be static or moverelative to the cleaning zone while the cleaning zone cleans thedeposition head. The cleaning zone may comprise a wiper, a nozzleconfigured to provide at least one cleaning solvent, or both. The wiperof the cleaning zone may be a blade (e.g., a doctor blade), a roller, ora rod. In some cases, one or more wipers of the cleaning zone may comein contact with one or more wipers of the deposition head and remove anyexcess resin remaining on the one or more wipers of the deposition head.In some cases, one or more nozzles of the cleaning zone may dispense orjet the at least one cleaning solvent to the one or more wipers of thedeposition head for cleaning. The one or more nozzles of the cleaningzone may be in fluid communication with at least one source of the atleast one cleaning solvent. At least a portion of the viscous liquid maybe soluble in the at least one cleaning solvent. The cleaning zone maycomprise a repository that can hold the excess viscous liquid that isremoved from the deposition head and/or the at least one cleaningsolvent.

The method may comprise providing a repository (e.g., vat or container)adjacent to the open platform. The repository may be configured tocollect the viscous liquid from the film of the deposition head. Therepository may be configured to hold any excess viscous liquid that isremoved from the print window by the deposition head. After removing anyexcess viscous liquid from the print window, the deposition head maymove and use at least one wiper to collect the excess viscous liquidinto the repository. The repository may be a recycling bin. Therepository may be in fluid communication with the source of the viscousliquid to recycle the collected excess viscous liquid for printing.Alternatively or in addition to, the collected excess viscous liquid maybe removed for reprocessing. The reprocessing of the collected excessviscous liquid may comprise (i) filtering out any polymerized solidparticulates, (ii) filtering out any of the plurality of particles thatmay be greater than a target particle size, (iii) remixing the viscousliquid to ensure homogeneity, and/or (iv) removing at least a portion ofair entrapped in the viscous liquid. In some cases, the at least theportion of air entrapped in the viscous liquid may be removed bycentrifuging the viscous liquid. In some cases, the repository maycomprise a sensor (e.g., an optical sensor or a weight scale) to detectwhen the repository is full and/or when an amount of the collectedexcess viscous liquid is above a predefined threshold.

The method may comprise providing a transparent film adjacent to theopen platform and configured to hold the film of the viscous liquid. Thetransparent film may cover the print window. The transparent film maycomprise one or more fluoropolymers that reduce adhesion of a curedportion of the viscous liquid on the transparent film. Examples of theone or more fluoropolymers include polyvinylidene fluoride (PVDF),ethylenchlorotrifluoroethylene (ECTFE), ethylenetetrafluoroethylene(ETFE), polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), andmodified fluoroalkoxy (a copolymer of tetrafluoroethylene andperfluoromethylvinylether, also known as MFA). The transparent film mayreduce or eliminate any undesirable force (e.g., a sliding or rotationalmechanism) that may otherwise be needed to separate the cured portion ofthe viscous liquid and the print window. This may yield a reducedfailure rate and increased printing speed.

The method may comprise providing a motion stage adjacent to the openplatform. The motion stage may be coupled to the deposition head andconfigured to direct movement of the deposition head across the openplatform. In addition, the motion stage may be coupled to one or moreother components of the system that move across the platform (e.g., anadditional deposition head, a sensor, etc.). The motion stage may beconnected to an actuator that is configured to direct movement of themotion stage. The actuator may be a mechanical, hydraulic, pneumatic,electro-mechanical, or magnetic actuator. The controller may beoperatively coupled to the actuator to control movement of the motionstage. Alternatively or in addition to, the system may comprise anadditional motion stage coupled to the open platform to direct movementof the open platform relative to other components of the system.

The method may comprise providing the optical source that provides thelight through the print window for curing the at least the portion ofthe film of the viscous liquid. In some cases, the light of the opticalsource may comprise a first wavelength for curing the photoactive resinin a first portion of the film of the viscous liquid. The firstwavelength may activate the at least one photoinitiator of thephotoactive resin, thereby initiating curing of the polymeric precursorsinto the polymeric material. The light may be a photoinitiation light,and the first portion of the film may be a photoinitiation layer. Theoptical source may provide a different light having a third wavelengthfor inhibiting curing of the photoactive resin in a second portion ofthe film of the viscous liquid. The first wavelength and the thirdwavelength may be different. The third wavelength may activate the atleast one photoinhibitor of the photoactive resin, thereby inhibitingcuring of the polymeric precursors into the polymeric material. Thedifferent light may be a photoinhibition light, and the second portionof the film of the viscous liquid may be a photoinhibition layer. Insome cases, a dual-wavelength projector (e.g., a dual-wavelength laser)may be used as the optical source that provides both the photoinitiationlight and the photoinhibition light.

In some cases, the light of the optical source may comprise a firstwavelength for curing the photoactive resin in a first portion of thefilm of the viscous liquid. The first wavelength may activate the atleast one photoinitiator of the photoactive resin, thereby initiatingcuring of the polymeric precursors into the polymeric material. Thelight may be a photoinitiation light, and the first portion of the filmmay be a photoinitiation layer. The light may be a patterned light. Themethod may further comprise providing a different optical sourcecomprising a different light having a third wavelength for inhibitingcuring of the photoactive resin in a second portion of the film of theviscous liquid. The first wavelength and the third wavelength may bedifferent. The third wavelength may activate the at least onephotoinhibitor of the photoactive resin, thereby inhibiting curing ofthe polymeric precursors into the polymeric material. The differentlight may be a photoinhibition light, and the second portion of the filmof the viscous liquid may be a photoinhibition layer. The differentlight may be a flood light. The photoinhibition layer may preventadhesion of the cured polymeric material to the print window (or to thetransparent film on or adjacent to the print window).

The optical source that directs the photoinitiation light may be amask-based display, such as a liquid crystal display (LCD) device, orlight emitting, such as a discrete light emitting diode (LED) arraydevice. Alternatively, the optical source that directs thephotoinitiation light may be a digital light processing (DLP) device,including a digital micro-mirror device (DMD) for producing patternedlight that can selectively illuminate and cure 3D printed structures.The initiation light directed from the DLP device may pass through oneor more projection optics (e.g., a light projection lens) prior toilluminating through the print window and to the film of the viscousliquid. The one or more projection optics may be integrated in the DLPdevice. Alternatively or in addition to, the one or more projectionoptics or may be configured between the DLP device and the print window.A relative position of the one or more projection optics relative to theDLP device and the print window may be adjustable to adjust an area ofthe photoinitiation layer in the film of the viscous liquid. The area ofthe photoinitiation layer may be defined as a build area. In some cases,the one or more projection optics may be on a projection opticsplatform. The projection optics platform may be coupled to an actuatorthat directs movement of the projection optics platform. The controllermay be operatively coupled to the actuator to control movement of theprojection optics platform. The controller may direct the actuator(e.g., a screw-based mechanism) to adjust a relative position of the oneor more projection optics to the DLP device and the print window duringprinting the 3D object.

The different optical source that directs the photoinhibition light maycomprise a plurality of light devices (e.g., a plurality of lightemitting diodes (LEDs)). The light devices may be on a light platform.The light platform may be configured (i) move relative to the printwindow and (ii) yield a uniform projection of the photoinhibition lightwithin the photoinhibition layer in the film of the viscous liquidadjacent to the print window. In some cases, the position of the lightplatform may be independently adjustable with respect to a position ofthe optical source that directs the photoinitiation light. The lightplatform comprising the plurality of light devices may be arranged withrespect to the print window such that a peak intensity of each of theplurality of light devices is directed at a different respectiveposition (e.g., corner or other position) of the build area. In anexample, the build area may have four corners and a separate beam oflight (e.g., a separate LED) may be directed to each corner of the buildarea. The beams of photoinhibition light from the plurality of lightdevices may overlap to provide the uniform projection of thephotoinhibition light within the photoinhibition layer. The lightplatform may be coupled to an actuator that directs movement of thelight platform. The controller may be operatively coupled to theactuator to control movement of the light platform. The controller maydirect the actuator (e.g., a screw-based mechanism) to adjust a relativeposition of the plurality of light devices to the print window duringprinting the 3D object. In some cases, the one or more projection opticsto the DLP device (for the photoinitiation light) may be on the lightplatform.

Whether using one, two, or more optical sources, the photoinhibitionlight may be configured to create the photoinhibition layer in the filmof the viscous liquid adjacent to the print window. In some cases, thephotoinhibition light may be configured to form the photoinhibitionlayer in the film of the viscous liquid adjacent to the transparent filmthat is covering the print window. Furthermore, the photoinitiationlight may be configured to cure the photoactive resin in thephotoinitiation layer that resides between the photoinhibition layer andthe build head. The photoactive resin in the photoinitiation layer maybe cured into at least a portion of the 3D structure. In some cases, thephotoinitiation light may be configured to cure the photoactive resin inthe photoinitiation layer that resides between the photoinhibition layerand the at least the portion of the 3D structure adjacent to the buildhead.

A thickness of the photoinitiation layer, the photoinhibition layer, orboth may be adjusted by adjusting an intensity and duration of thephotoinitiation light, the photoinhibition light, or both. The thicknessof the photoinitiation layer, the photoinhibition layer, or both may beadjusted to adjust the thickness of the printed layer of the at leastthe portion of the 3D object. Alternatively or in addition to, thethickness of the photoinitiation layer, the photoinhibition layer, orboth may be adjusted by adjusting the speed at which the build headmoves away in a direction away from the print window.

The addition light source (i.e. sensor light source) that directs theadditional light (i.e., sensor light) may comprise a plurality of lightdevices (e.g., a plurality of light emitting diodes (LEDs)). The lightdevices may be on a light platform. In some cases, the light platformmay be configured (i) move relative to the print window and (ii) yield auniform projection of the sensor light within the film of the viscousliquid adjacent to the print window. In some cases, the position of thelight platform may be independently adjustable with respect to aposition of the optical source that directs the photoinitiation light.The light platform comprising the plurality of light devices fordirecting the sensor light may be arranged with respect to the printwindow such that a peak intensity of each of the plurality of lightdevices is directed at a different respective position (e.g., corner orother position) of the build area. In an example, the build area mayhave four corners and a separate beam of light (e.g., a separate LED)may be directed to each corner of the build area. The beams of sensorlight from the plurality of light devices may overlap to provide theuniform projection of the sensor light within the photoinhibition layer.The light platform may be coupled to an actuator that directs movementof the light platform. The controller may be operatively coupled to theactuator to control movement of the light platform. The controller maydirect the actuator (e.g., a screw-based mechanism) to adjust a relativeposition of the plurality of light devices to the print window duringprinting the 3D object. In some cases, the one or more projection opticsto the DLP device (for the photoinitiation light) may be on the lightplatform. In some cases, the additional optical source for directing thephotoinhibition light and the sensor light source may be on a same lightplatform. In some cases, the additional optical source for directing thephotoinhibition light and the sensor light source may be on differentlight platforms.

Once the at least the portion of the 3D object is printed (hereinreferred to as a green body), the method may further comprise removingthe green body from the build head. The green body may be separated fromthe build head by inserting a thin material (e.g. a steel blade) betweenthe green body and the build head. In some cases, a first layer of thegreen body that is in contact with the build head may not comprise theplurality of particles for easy removal from the build head by the thinmaterial. The method may further comprise washing the green body. Insome cases, the green body may be washed by jetting a solvent (e.g.,isopropanol) to remove any excess polymeric precursor.

The method may further comprise subjecting the green body comprising atleast the polymeric material to heating (e.g., in a furnace), to therebyheat at least the plurality of particles encapsulated in the at leastthe polymeric material. The heating may be under conditions sufficientto sinter the plurality of particles to form a final product that is atleast a portion of a 3D object or an entire 3D object. During heating(e.g., sintering), the organic components (e.g., the polymeric material,additives, etc.) may decompose and leave the green body. At least aportion of the decomposed organic components may leave the green body ingas phase.

The green body may be heated in a processing chamber. The temperature ofthe processing temperature may be regulated with at least one heater.The processing chamber may be an oven or a furnace. The oven or furnacemay be heated with various heating approaches, such as resistiveheating, convective heating and/or radiative heating. Examples of thefurnace include an induction furnace, electric arc furnace, gas-firedfurnace, plasma arc furnace, microwave furnace, and electric resistancefurnace. Such heating may be employed at a fixed or variating heatingrate from an initial temperature to a target temperature or temperaturerange.

A green body comprising metallic and/or intermetallic particles may beheated from room temperature to a processing temperature. The processingtemperature may be kept constant or substantially constant for a givenperiod of time, or may be adjusted to one or more other temperatures.The processing temperature may be selected based on the material of theparticles in the green body (e.g., the processing temperature may behigher for material having a higher melting point than other materials).The processing temperature may be sufficient to sinter but notcompletely melt the particles in the green body. As an alternative, theprocessing temperature may be sufficient to melt the particles in thegreen body.

The processing temperature for heating (e.g., sintering) the green body(including the metal and/or intermetallic particles) may range betweenabout 300 degrees Celsius to about 2200 degrees Celsius. The processingtemperature for sintering the green body may be at least about 300degrees Celsius, 350 degrees Celsius, 400 degrees Celsius, 450 degreesCelsius, 500 degrees Celsius, 550 degrees Celsius, 600 degrees Celsius,650 degrees Celsius, 700 degrees Celsius, 750 degrees Celsius, 800degrees Celsius, 850 degrees Celsius, 900 degrees Celsius, 950 degreesCelsius, 1000 degrees Celsius, 1050 degrees Celsius, 1100 degreesCelsius, 1150 degrees Celsius, 1200 degrees Celsius, 1250 degreesCelsius, 1300 degrees Celsius, 1350 degrees Celsius, 1400 degreesCelsius, 1450 degrees Celsius, 1500 degrees Celsius, 1550 degreesCelsius, 1600 degrees Celsius, 1700 degrees Celsius, 1800 degreesCelsius, 1900 degrees Celsius, 2000 degrees Celsius, 2100 degreesCelsius, 2200 degrees Celsius, or more. The processing temperature forsintering the green body (including the particles) may be at most about2200 degrees Celsius, 2100 degrees Celsius, 2000 degrees Celsius, 1900degrees Celsius, 1800 degrees Celsius, 1700 degrees Celsius, 1600degrees Celsius, 1550 degrees Celsius, 1500 degrees Celsius, 1450degrees Celsius, 1400 degrees Celsius, 1350 degrees Celsius, 1300degrees Celsius, 1250 degrees Celsius, 1200 degrees Celsius, 1150degrees Celsius, 1100 degrees Celsius, 1050 degrees Celsius, 1000degrees Celsius, 950 degrees Celsius, 900 degrees Celsius, 850 degreesCelsius, 800 degrees Celsius, 750 degrees Celsius, 700 degrees Celsius,650 degrees Celsius, 600 degrees Celsius, 550 degrees Celsius, 500degrees Celsius, 450 degrees Celsius, 400 degrees Celsius, 350 degreesCelsius, 300 degrees Celsius, or less.

In an example, a green body comprising aluminum particles may be heatedfrom room temperature to a processing temperature ranging between about350 degrees Celsius to about 700 degrees Celsius. In another example, agreen body comprising copper particles may be heated from roomtemperature to a processing temperature of about 1000 degrees Celsius.In another example, a green body comprising stainless steel particlesmay be heated from room temperature to a processing temperature rangingbetween about 1200 degrees Celsius to about 1500 degrees Celsius. Inanother example, a green body comprising other tool steel particles maybe heated from room temperature to a processing temperature of about1250 degrees Celsius. In another example, a green body comprisingtungsten heavy alloy particles may be heated from room temperature to aprocessing temperature of about 1500 degrees Celsius.

During sintering the green body comprising the metallic and/orintermetallic particles, the temperature of the processing chamber maychange at a rate ranging between about 0.1 degrees Celsius per minute(degrees Celsius/min) to about 200 degrees Celsius/min. The temperatureof the processing chamber may change at a rate of at least about 0.1degrees Celsius/min, 0.2 degrees Celsius/min, 0.3 degrees Celsius/min,0.4 degrees Celsius/min, 0.5 degrees Celsius/min, 1 degrees Celsius/min,2 degrees Celsius/min, 3 degrees Celsius/min, 4 degrees Celsius/min, 5degrees Celsius/min, 6 degrees Celsius/min, 7 degrees Celsius/min, 8degrees Celsius/min, 9 degrees Celsius/min, 10 degrees Celsius/min, 20degrees Celsius/min, 50 degrees Celsius/min, 100 degrees Celsius/min,150 degrees Celsius/min, 200 degrees Celsius/min, or more. Thetemperature of the processing chamber may change at a rate of at mostabout 200 degrees Celsius/min, 150 degrees Celsius/min, 100 degreesCelsius/min, 50 degrees Celsius/min, 20 degrees Celsius/min, 10 degreesCelsius/min, 9 degrees Celsius/min, 8 degrees Celsius/min, 7 degreesCelsius/min, 6 degrees Celsius/min, 5 degrees Celsius/min, 4 degreesCelsius/min, 3 degrees Celsius/min, 2 degrees Celsius/min, 1 degreesCelsius/min, 0.5 degrees Celsius/min, 0.4 degrees Celsius/min, 0.3degrees Celsius/min, 0.2 degrees Celsius/min, 0.1 degrees Celsius/min,or less.

In some cases, during sintering the green body comprising the metallicand/or intermetallic particles, the process may comprise holding at afixed temperature between room temperature and the processingtemperature for a time ranging between about 1 min to about 240 min. Thesintering process may comprise holding at a fixed temperature for atleast about 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 90 min, 120min, 150 min, 180 min, 210 min, 240 min, or more. The sintering processmay comprise holding at a fixed temperature for at most about 240 min,210 min, 180 min, 150 min, 120 min, 90 min, 60 min, 50 min, 40 min, 30min, 20 min, 10 min, 1 min, or less. In some cases, during the sinteringprocess, the temperature may not be held at a processing temperature foran extended period of time (e.g., once a target temperature is reached,the temperature may be reduced). In an example, the sintering processmay increase the temperature to a first temperature and immediately(e.g., without holding at the first temperature for a period of time)lower the temperature to a second temperature that is lower than thefirst temperature.

A green body comprising ceramic particles may be heated from roomtemperature to a processing temperature ranging between about 900degrees Celsius to about 2000 degrees Celsius. The processingtemperature may be kept constant or substantially constant for a givenperiod of time, or may be adjusted to one or more other temperatures.The processing temperature for sintering the green body (including theparticles) may be at least about 900 degrees Celsius, 950 degreesCelsius, 1000 degrees Celsius, 1050 degrees Celsius, 1100 degreesCelsius, 1150 degrees Celsius, 1200 degrees Celsius, 1300 degreesCelsius, 1400 degrees Celsius, 1500 degrees Celsius, 1600 degreesCelsius, 1700 degrees Celsius, 1800 degrees Celsius, 1900 degreesCelsius, 2000 degrees Celsius, or more. The processing temperature forsintering the green body may be at most about 2000 degrees Celsius, 1900degrees Celsius, 1800 degrees Celsius, 1700 degrees Celsius, 1600degrees Celsius, 1500 degrees Celsius, 1400 degrees Celsius, 1300degrees Celsius, 1200 degrees Celsius, 1150 degrees Celsius, 1100degrees Celsius, 1050 degrees Celsius, 1000 degrees Celsius, 950 degreesCelsius, 900 degrees Celsius, or less.

In an example, a green body comprising alumina particles may be heatedfrom room temperature to a processing temperature ranging between about1500 degrees Celsius to about 1950 degrees Celsius. In an example, agreen body comprising cemented carbide particles may be heated from roomtemperature to a processing temperature ranging between about 1700degrees Celsius. In an example, a green body comprising zirconiaparticles may be heated from room temperature to a processingtemperature ranging between about 1100 degrees Celsius.

During sintering the green body comprising the ceramic particles, thetemperature of the processing chamber may change at a rate rangingbetween about 0.1 degrees Celsius per minute (degrees Celsius/min) toabout 200 degrees Celsius/min. The temperature of the processing chambermay change at a rate of at least about 0.1 degrees Celsius/min, 0.2degrees Celsius/min, 0.3 degrees Celsius/min, 0.4 degrees Celsius/min,0.5 degrees Celsius/min, 1 degrees Celsius/min, 2 degrees Celsius/min, 3degrees Celsius/min, 4 degrees Celsius/min, 5 degrees Celsius/min, 6degrees Celsius/min, 7 degrees Celsius/min, 8 degrees Celsius/min, 9degrees Celsius/min, 10 degrees Celsius/min, 20 degrees Celsius/min, 50degrees Celsius/min, 100 degrees Celsius/min, 150 degrees Celsius/min,200 degrees Celsius/min, or more. The temperature of the processingchamber may change at a rate of at most about 200 degrees Celsius/min,150 degrees Celsius/min, 100 degrees Celsius/min, 50 degreesCelsius/min, 20 degrees Celsius/min, 10 degrees Celsius/min, 9 degreesCelsius/min, 8 degrees Celsius/min, 7 degrees Celsius/min, 6 degreesCelsius/min, 5 degrees Celsius/min, 4 degrees Celsius/min, 3 degreesCelsius/min, 2 degrees Celsius/min, 1 degrees Celsius/min, 0.5 degreesCelsius/min, 0.4 degrees Celsius/min, 0.3 degrees Celsius/min, 0.2degrees Celsius/min, 0.1 degrees Celsius/min, or less.

In some cases, during sintering the green body comprising the ceramicparticles, the process may comprise holding at a fixed temperaturebetween room temperature and the processing temperature for a timeranging between about 1 min to about 240 min. The sintering process maycomprise holding at a fixed temperature for at least about 1 min, 10min, 20 min, 30 min, 40 min, 50 min, 60 min, 90 min, 120 min, 150 min,180 min, 210 min, 240 min, or more. The sintering process may compriseholding at a fixed temperature for at most about 240 min, 210 min, 180min, 150 min, 120 min, 90 min, 60 min, 50 min, 40 min, 30 min, 20 min,10 min, 1 min, or less. In some cases, during the sintering process, thetemperature may not be held at a processing temperature for an extendedperiod of time (e.g., once a target temperature is reached, thetemperature may be reduced). In an example, the sintering process mayincrease the temperature to a first temperature and immediately (e.g.,without holding at the first temperature for a period of time) lower thetemperature to a second temperature that is lower than the firsttemperature.

During sintering the green body comprising the plurality of particles(e.g. metal, intermetallic, and/or ceramic), the green body may besubjected to cooling by a fluid (e.g., liquid or gas). The fluid may beapplied to the green body and/or the processing chamber to decrease thetemperature of the green body. The fluid may be subjected to flow uponapplication of positive or negative pressure. Examples of the fluid forcooling the green body include water, oil, hydrogen, nitrogen, argon,etc. Cooling the green body during the sintering process may controlgrain size within the sintered body.

The controller may be configured to control various parts (e.g.,actuators, sensors, etc.) of different components of the 3D printingsystem, as described in detail above.

In another aspect, the present disclosure provides a system for printinga 3D object. The system may comprise a build surface configured toretain a film comprising a polymeric precursor. The system may comprisea sensor in sensing communication with the build surface. The system maycomprise a light source in optical communication with the build surface,wherein the light source is configured to provide light. The system maycomprise a controller comprising a circuit operatively coupled to thesensor and the light source, wherein the controller is configured to (i)use the sensor to determine a profile of the film, which profile isindicative of a quality of the film, and (ii) determine if the profilemeets a quality threshold, and (iii) subsequent to (ii), (1) if saidprofile meets a quality threshold, direct said light source to expose atleast a portion of said film to said light to initiate formation of apolymeric material from said polymeric precursor, thereby printing atleast a portion of said 3D object, or (2) if said profile does not meetsaid quality threshold, direct said film to be adjusted or redeposited.The profile may be a feature of the film. The systems disclosed hereinmay utilize all components and configurations described in methods forprinting a 3D object of the present disclosure.

The controller may be further configured to (i) expose the film to anadditional light (i.e., a sensor light) and (ii) use the sensor todetect at least a portion of the additional light that is transmittedthrough the film. The light (i.e., the photoinitiation light) may have afirst wavelength and the additional light may have a second wavelength.The second wavelength of the sensor light may be different than thefirst wavelength of the photoinitiation light. In an example, the secondwavelength of the sensor light and the first wavelength of thephotoinitiation light are different. The light source (i.e., aphotoinitiation light source) may be configured to provide theadditional light. Alternatively or in addition to, an additional lightsource (i.e., a sensor light source) may be configured to provide theadditional light.

The system may further comprise an optical diffuser located adjacent tothe build surface and away from the film. The optical diffuser may beconfigured to diffuse the additional light before at least a portion ofthe light reaches the sensor. The optical diffuser may be disposed (i)between a source of the additional light and the film comprising thepolymeric precursor, and/or (ii) between the film comprising thepolymeric precursor and the sensor.

During use, the film comprising the polymeric precursor may furthercomprise a plurality of particles. The plurality of particles may be atleast one metal particle, at least one ceramic particle, or acombination thereof. The plurality of particles may be usable forprinting the at least the portion of the 3D object. During use, once atleast a portion of the polymeric precursor in the film is formed intothe polymeric material, the polymeric material may encapsulate theplurality of particles. During use, the film may further comprise (i) aphotoinitiator that initiates formation of the polymeric material fromthe polymeric precursor away from the print window, and (ii) aphotoinhibitor that inhibits formation of the polymeric material fromthe polymeric precursor adjacent to the print window. The polymericmaterial formed from at least a portion of the polymeric precursor inthe film may encapsulate other components of the film, such as, forexample, photoinitiator(s), photoinhibitor(s), light absorber(s),binder(s), etc.

During use, the film comprising the polymeric precursor may furthercomprise at least one metal particle, at least one ceramic particle, ora combination thereof.

The system may further comprise a build head configured to move relativeto the build surface and hold the at least the portion of the 3D object.The system may further comprise a deposition head adjacent to the buildsurface and configured to move across the build surface to deposit thefilm adjacent to the build surface. The build surface may comprise aprint window configured to retain the film. The build surface may bepart of a vat that is configured to retain the film. The build surfacemay be part of an open platform that is configured to retain the film.

FIGS. 1A to 1D show examples of a 3D printing system 100. Referring toFIG. 1A, the system 100 includes an open platform 101 comprising a printwindow 102 to hold a film of a viscous liquid 104, which includes aphotoactive resin. The photoactive resin includes a polymeric precursorthat is configured to form a polymeric material. The open platform 101may be a build surface for depositing the film 104 comprising thepolymeric precursor, as well as for printing at least a portion of the3D object. The viscous liquid of the film 104 may also include aplurality of particles (e.g., metal, intermetallic, ceramic, and/orpolymeric particles). The system 100 includes a deposition head 105 thatcomprises a nozzle 107 that is in fluid communication with a source ofthe viscous liquid 109. The source of the viscous liquid 109 may be asyringe. The syringe may be operatively coupled to a syringe pump. Thesyringe pump can direct the syringe in a positive direction (from thesource of the viscous liquid 109 towards the nozzle 107) to dispense theviscous liquid. The syringe pump can direct the syringe in a negativedirection (away from the nozzle 107 towards the source of the viscousliquid 109) to retract any excess viscous liquid in the nozzle and/or onthe print window back into the syringe. The deposition head 105 isconfigured to move across the open platform 101 comprising the printwindow 102 to deposit the film of the viscous liquid 104. In some cases,the system 100 may comprise an additional source of an additionalviscous liquid that is in fluid communication with the nozzle 107 or anadditional nozzle of the deposition head 105. In some cases, the system100 may comprise an additional deposition head comprising an additionalnozzle that is in fluid communication with an additional source of anadditional viscous liquid. In some cases, the system 100 may comprisethree or more deposition heads and three or more sources of the same ordifferent viscous liquids.

Referring to FIG. 1A, the system 100 includes one or more sensors 150 insensing communication with the open platform 101 comprising the printwindow 102. The sensor(s) 150 may be operatively coupled to a controllercomprising a circuit. The sensor(s) 150 are configured to determine aprofile of the film 104, which profile is indicative of a quality of thefilm 104. Examples of the profile of the film 104 include thickness,width, area, volume, shape, densitometry (e.g., density of one or moreparticles), and defects. The system 100 also includes one or more sensorlight sources 152 in in optical communication with the open platform 101comprising the print window 102. The sensor light source(s) 152 areconfigured to provide one or more sensor lights 160 that are to be usedby the sensor(s) 150 to at least determine the profile of the film 104.The sensor light source(s) 152 can be arranged on a light platform 138.The light platform 138 is mounted on adjustable axis rails 140. Theadjustable axis rails 140 allow for movement of the light platform 138along an axis towards or away from the print window 102. A relativeposition of the light platform 138 comprising the sensor light source(s)152 may be adjusted to project the sensor light(s) 160 into the film 104at the respective peak intensity and/or in a uniform projection manner.In some cases, the light platform 138 functions as a heat-sink for atleast the sensor light source(s) 152 arranged on the light platform 138.In some cases, the sensor light(s) 160 may be directed to the openplatform 101 non-uniformly (e.g., provided with bright spotscorresponding to location(s) of the sensor light source(s) 152. Thus,the system includes one or more diffusers 155 that are movable relativeto the sensor light source(s) 152 and the print window 102 of the openplatform 101. The diffuser(s) 155 may be located adjacent to the buildsurface and away from the film 104. The diffuser(s) 155 are configuredto cause the sensor light(s) 160 to spread evenly across a surface ofthe diffuser(s) 155, thereby minimizing or removing high intensitybright spots as the sensor light(s) 160 travel through the diffuser(s)155. Thus, the non-diffused sensor light(s) 160 pass through thediffuser(s) 155 and are directed to the print window 102 as diffusedsensor light(s) 162. The sensor(s) 150 are in sensing communication witha sensing zone 164 adjacent to open platform 101 comprising the printwindow 102. After the film 104 is printed, the diffused sensor light(s)162 are directed to the print window 102, and the sensor(s) 150 isconfigured to detect (e.g., measure, capture one or more images of,etc.) at least a portion of the sensor light(s) 162 that is transmittedthrough (i) the print window 102 and/or (ii) the print window 102 andthe film 104. The sensor light source(s) 152 may provide one or more IRor visible light(s). The sensor(s) may detect an optical densitometryprofile of the film 104 to provide a feedback on the profile of the film104.

Referring to FIG. 1B, if the profile of the film 104, as detected by thesensor(s) 150, meets a quality threshold (e.g., as determined by thecontroller operatively coupled to the sensor(s) 150), the diffuser(s)155 may be moved away from the print window 102, the sensor lightsource(s) be may be turned off, the build head 110 may be moved towardsto film 104 on or adjacent to the print window 102, and a differentillumination may be transmitted through the print window 102 to cure atleast a portion of the film of the viscous liquid 104 to print at leasta portion of a 3D structure. The diffuser(s) 155 may be moved away fromthe print window 102 to prevent interference with the illumination forcuring (and illumination for inhibition of curing). Such differentillumination may cure at least a portion of the film of the viscousliquid 104 to print at least a portion of a 3D structure on a previouslyprinted object 108 that is coupled to the build head 110. The previouslyprinted object 108 is shown as a block. However, in practice, a widevariety of complicated shapes may be printed. In some cases, the atleast the portion of the 3D structure 108 includes entirely solidstructures, hollow core prints, lattice core prints, and generativedesign geometries. The at least the portion of the 3D structure 108 isprinted on a build head 110, which is connected by a rod 112 to one ormore 3D printing mechanisms 114. The 3D printing mechanisms 114 mayinclude various mechanical structures for moving the build head 110 in adirection towards and/or away from the open platform 101. This movementis a relative movement, and thus moving pieces can be the build head110, the open platform 101, or both, in various embodiments. In somecases, the 3D printing mechanisms 114 include Cartesian (xyz) type 3Dprinter motion systems or delta type 3D printer motion systems. In somecases, the 3D printing mechanisms 114 include one or more controllers todirect movement of the build head 110, the open platform 101, or both.

Referring to FIG. 1B, multiple devices emitting various wavelengthsand/or intensities of light, including a light projection device 126 andlight sources 128, may be positioned below the print window 102 and incommunication with the one or more controllers. In some cases, the lightsources 128 can include at least 2, 3, 4, 5, 6, or more light sources.As an alternative to the light sources 128, a single light source may beused. The light projection device 126 directs a light having a firstwavelength through the print window 102 and into the film of the viscousliquid 104 adjacent to the print window 102. The first wavelengthemitted by the light projection device 126 is selected to producephotoinitiation and is used to create at least a portion of the 3Dstructure on the at least the portion of the 3D structure 108 that isadjacent to the build head 110 by curing the photoactive resin in thefilm of the viscous liquid 104 within a photoinitiation layer 130. Insome cases, the light projection device 126 is utilized in combinationwith one or more projection optics 132 (e.g. a projection lens for adigital light processing (DLP) device), such that the light output fromthe light projection device 126 passes through the one or moreprojection optics 132 prior to illuminating the film of the viscousliquid 104 adjacent to the print window 102.

Referring to FIG. 1B, in some cases, the light projection device 126 isa DLP device including a digital micro-mirror device (DMD) for producingpatterned light that can selectively illuminate and cure the photoactiveresin in the photoinitiation layer 130. The light projection device 126,in communication with the one or more controllers, may receiveinstructions defining a pattern of illumination to be projected from thelight projection device 126 into the photoinitiation layer 130 to cure alayer of the photoactive resin onto the at least the portion of the 3Dstructure 108.

Referring to FIG. 1B, the light sources 128 direct a different lighthaving a third wavelength into the film of the viscous liquid 104adjacent to the open platform 101 comprising the print window 102. Thedifferent light may be provided as multiple beams from the light sources128 through the print window 102 simultaneously. As an alternative, thedifferent light may be generated from the light sources 128 and providedas a single beam through the print window 102. The third wavelengthemitted by the light sources 128 is selected to produce photoinhibitionin the photoactive resin in the film of the viscous liquid 104 and isused to create a photoinhibition layer 134 within the film of theviscous liquid 104 directly adjacent to the print window 102. The lightsources 128 can produce a flood light to create the photoinhibitionlayer 134, the flood light being a non-patterned, high-intensity light.In some cases, the light sources 128 are light emitting diodes (LEDs)136. The light sources 128 can be arranged on the light platform 138.The light platform 138 is mounted on adjustable axis rails 140. Theadjustable axis rails 140 allow for movement of the light platform 138along an axis towards or away from the print window 102. The lightplatform 138 and the one or more projection optics 132 may be movedindependently. A relative position of the light platform 138 comprisingthe light sources may be adjusted to project the second light into thephotoinhibition layer 134 at the respective peak intensity and/or in auniform projection manner. In some cases, the light platform 138functions as a heat-sink for at least the light sources 128 arranged onthe light platform 138. The first wavelength of the light forphotoinitiation, the third wavelength of the different light forphotoinhibition, and a second wavelength of the sensor light(s) 160 (asshown in FIG. 1A) may be different. The light for photoinitiation, thedifferent light for photoinhibition, and the sensor light(s) 160 may beprovided by a same light source (e.g., a multi-wavelength laser) or twoor more different light sources. The different light for photoinhibitionand the sensor light(s) 160 may be provided by a same light source(e.g., a multi-wavelength laser) or different light sources. Thedifferent light for photoinhibition and the sensor light(s) 160 may bedisposed on the same light platform 138 or different light platforms.

Referring to FIG. 1B, the respective thicknesses of the photoinitiationlayer 130 and the photoinhibition layer 134 may be adjusted by the oneor more controllers. In some cases, this change in layer thickness(es)is performed for each new 3D printed layer, depending on the desiredthickness of the 3D printed layer, and/or the type of viscous liquid inthe film of the viscous liquid 104. The thickness(es) of thephotoinitiation layer 130 and the photoinhibition layer 134 may bechanged, for example, by changing the intensity of the respective lightemitting devices (126 and/or 128), exposure times for the respectivelight emitting devices, or both. In some cases, by controlling relativerates of reactions between the photoactive species (e.g., at least onephotoinitiator and at least one photoinhibitor), the overall rate ofcuring of the photoactive resin in the photoinitiation layer 130 and/orthe photoinhibition layer 134 may be controlled. This process can thusbe used to prevent curing from occurring at the film of the viscousliquid-print window interface and control the rate at which curing ofthe photoactive resin takes place in the direction normal to the film ofthe photoactive resin-print window interface.

Referring to FIG. 1C, once the at least the portion of the 3D object 170is printed and coupled to the previously printed object 108 on the buildhead 110, the build head 110 is moved away from the remainder 172 of thefilm 104 on or adjacent to the print window 102. The remainder 172 ofthe film 104 comprises excess viscous liquid from the film 104. Thediffuser(s) is moved back towards the print window 102. The sensor lightsource(s) 152 provide the sensor light(s) 160, which sensor light(s) 160are transmitted through the diffuser 155 and directed as diffusedlight(s) 162 towards the print window 102. The sensor(s) 150 in sensingcommunication with the sensing zone 164 detect (e.g., measure, captureone or more images of, etc.) at least a portion of the diffused sensorlight(s) 162 that is transmitted through (i) the print window 102 and/or(ii) the print window 102 and the remainder 172 of the film 104, therebyto obtain a negative image (e.g., a silhouette image) of the recentlyprinted portion 170 of the 3D object. The negative image may be used toassess whether or not the portion 170 of the 3D object was printed inaccordance to a computer model of the 3D object (e.g., by thecontroller). In some cases, the controller may determine that, based atleast in part on the negative image, the portion 170 of the 3D objectwas printed in accordance to the computer model of the 3D object. Insuch a case, the controller may direct the deposition head 105 to removethe remainder 172 of the film 104 from the print window 102, and deposita new film of the viscous liquid to print a subsequent portion (e.g.,layer) of the 3D object. In some cases, the controller may determinethat, based at least in part on the negative image, the portion 170 ofthe 3D object was not printed in accordance to the computer model of the3D object. In such a case, the controller may direct the deposition head105 to remove the remainder 172 of the film 104 from the print window102, and deposit a new film of the viscous liquid to re-print theprevious layer or print a sub-portion of the previous layer that was notprinted as part of the portion 170 of the 3D object.

Referring to FIG. 1D, once the film 104 or the remainder 172 of the film104 is removed from the print window (e.g., by the deposition head 105),the diffused sensor light(s) 162 from the sensor light sources(s) 152may be directed to the print window 102. The sensor(s) 150 in sensingcommunication with the sensing zone 164 may detect (e.g., measure,capture one or more images of, etc.) at least a portion of the diffusedsensor light(s) 162 that is transmitted through the print window 102 todetermine quality of the print window 102 prior to depositing a new filmof the viscous liquid.

Computer Systems

The present disclosure provides computer systems that are programmed toimplement methods of the disclosure. Computer systems of the presentdisclosure may be used to regulate various operations of 3D printing,such as providing a film of a viscous liquid adjacent to an openplatform and directing a sensor to determine a profile of the film,which profile is indicative of a quality of the film.

FIG. 8 shows a computer system 801 that is programmed or otherwiseconfigured to communicate with and regulate various aspects of a 3Dprinter of the present disclosure. The computer system 801 cancommunicate with the light sensor(s), light sources (e.g., the sensorlight source(s)), diffuser, build head, one or more deposition heads, orone or more sources of one or more viscous liquids of the presentdisclosure. The computer system 801 may also communicate with the 3Dprinting mechanisms or one or more controllers of the presentdisclosure. The computer system 801 can be an electronic device of auser or a computer system that is remotely located with respect to theelectronic device. The electronic device can be a mobile electronicdevice.

The computer system 801 includes a central processing unit (CPU, also“processor” and “computer processor” herein) 805, which can be a singlecore or multi core processor, or a plurality of processors for parallelprocessing. The computer system 801 also includes memory or memorylocation 810 (e.g., random-access memory, read-only memory, flashmemory), electronic storage unit 815 (e.g., hard disk), communicationinterface 820 (e.g., network adapter) for communicating with one or moreother systems, and peripheral devices 825, such as cache, other memory,data storage and/or electronic display adapters. The memory 810, storageunit 815, interface 820 and peripheral devices 825 are in communicationwith the CPU 805 through a communication bus (solid lines), such as amotherboard. The storage unit 815 can be a data storage unit (or datarepository) for storing data (i.e., a database). The computer system 801can be operatively coupled to a computer network (“network”) 830 withthe aid of the communication interface 820. The network 830 can be theInternet, an internet and/or extranet, or an intranet and/or extranetthat is in communication with the Internet. The network 830 in somecases is a telecommunication and/or data network. The network 830 caninclude one or more computer servers, which can enable distributedcomputing, such as cloud computing. The network 830, in some cases withthe aid of the computer system 801, can implement a peer-to-peernetwork, which may enable devices coupled to the computer system 801 tobehave as a client or a server.

The CPU 805 can execute a sequence of machine-readable instructions,which can be embodied in a program or software. The instructions may bestored in a memory location, such as the memory 810. The instructionscan be directed to the CPU 805, which can subsequently program orotherwise configure the CPU 805 to implement methods of the presentdisclosure. Examples of operations performed by the CPU 805 can includefetch, decode, execute, and writeback.

The CPU 805 can be part of a circuit, such as an integrated circuit. Oneor more other components of the system 801 can be included in thecircuit. In some cases, the circuit is an application specificintegrated circuit (ASIC).

The storage unit 815 can store files, such as drivers, libraries andsaved programs. The storage unit 815 can store user data, e.g., userpreferences and user programs. The computer system 801 in some cases caninclude one or more additional data storage units that are external tothe computer system 801, such as located on a remote server that is incommunication with the computer system 801 through an intranet or theInternet.

The computer system 801 can communicate with one or more remote computersystems through the network 830. For instance, the computer system 801can communicate with a remote computer system of a user. Examples ofremote computer systems include personal computers (e.g., portable PC),slate or tablet PC's (e.g., Apple® iPad, Samsung® Galaxy Tab),telephones, Smart phones (e.g., Apple® iPhone, Android-enabled device,Blackberry®), or personal digital assistants. The user can access thecomputer system 801 via the network 830.

Methods as described herein can be implemented by way of machine (e.g.,computer processor) executable code stored on an electronic storagelocation of the computer system 801, such as, for example, on the memory810 or electronic storage unit 815. The machine executable or machinereadable code can be provided in the form of software. During use, thecode can be executed by the processor 805. In some cases, the code canbe retrieved from the storage unit 815 and stored on the memory 810 forready access by the processor 805. In some situations, the electronicstorage unit 815 can be precluded, and machine-executable instructionsare stored on memory 810.

The code can be pre-compiled and configured for use with a machinehaving a processer adapted to execute the code, or can be compiledduring runtime. The code can be supplied in a programming language thatcan be selected to enable the code to execute in a pre-compiled oras-compiled fashion.

Aspects of the systems and methods provided herein, such as the computersystem 801, can be embodied in programming. Various aspects of thetechnology may be thought of as “products” or “articles of manufacture”typically in the form of machine (or processor) executable code and/orassociated data that is carried on or embodied in a type of machinereadable medium. Machine-executable code can be stored on an electronicstorage unit, such as memory (e.g., read-only memory, random-accessmemory, flash memory) or a hard disk. “Storage” type media can includeany or all of the tangible memory of the computers, processors or thelike, or associated modules thereof, such as various semiconductormemories, tape drives, disk drives and the like, which may providenon-transitory storage at any time for the software programming. All orportions of the software may at times be communicated through theInternet or various other telecommunication networks. Suchcommunications, for example, may enable loading of the software from onecomputer or processor into another, for example, from a managementserver or host computer into the computer platform of an applicationserver. Thus, another type of media that may bear the software elementsincludes optical, electrical and electromagnetic waves, such as usedacross physical interfaces between local devices, through wired andoptical landline networks and over various air-links. The physicalelements that carry such waves, such as wired or wireless links, opticallinks or the like, also may be considered as media bearing the software.As used herein, unless restricted to non-transitory, tangible “storage”media, terms such as computer or machine “readable medium” refer to anymedium that participates in providing instructions to a processor forexecution.

Hence, a machine readable medium, such as computer-executable code, maytake many forms, including but not limited to, a tangible storagemedium, a carrier wave medium or physical transmission medium.Non-volatile storage media include, for example, optical or magneticdisks, such as any of the storage devices in any computer(s) or thelike, such as may be used to implement the databas(es), etc. shown inthe drawings. Volatile storage media include dynamic memory, such asmain memory of such a computer platform. Tangible transmission mediainclude coaxial cables; copper wire and fiber optics, including thewires that comprise a bus within a computer system. Carrier-wavetransmission media may take the form of electric or electromagneticsignals, or acoustic or light waves such as those generated during radiofrequency (RF) and IR data communications. Common forms ofcomputer-readable media therefore include for example: a floppy disk, aflexible disk, hard disk, magnetic tape, any other magnetic medium, aCD-ROM, DVD or DVD-ROM, any other optical medium, punch cards papertape, any other physical storage medium with patterns of holes, a RAM, aROM, a PROM and EPROM, a FLASH-EPROM, any other memory chip orcartridge, a carrier wave transporting data or instructions, cables orlinks transporting such a carrier wave, or any other medium from which acomputer may read programming code and/or data. Many of these forms ofcomputer readable media may be involved in carrying one or moresequences of one or more instructions to a processor for execution.

The computer system 801 can include or be in communication with anelectronic display 835 that comprises a user interface (UI) 840 forproviding, for example, (i) activate or deactivate a 3D printer forprinting a 3D object, (ii) determining when to clean the depositionhead, or (iii) determine any defects in the film of the viscous liquid.Examples of UI's include, without limitation, a graphical user interface(GUI) and web-based user interface.

Methods and systems of the present disclosure can be implemented by wayof one or more algorithms. An algorithm can be implemented by way ofsoftware upon execution by the central processing unit 805. Thealgorithm can, for example, distinguish or differentiate one or moreprofiles (e.g., features, such as, for example, dimension(s), volume,shape, or pattern) of a film of the viscous liquid on or adjacent to thebuild surface based on a feedback from the sensor(s).

EXAMPLES

The examples below are illustrative and non-limiting.

Example 1

FIG. 2 shows an example of a 2D image 200 of the print window prior todeposition of the film of the viscous liquid, as captured by thesensor(s). IR light may be used as the sensor light(s). The print windowmay or may not include a transparent film (e.g., a fluorinated film) ona surface of the print window. The image 200 may be used as a backgroundimage of the print window when analyzing one or more images of the filmof the viscous liquid that is deposited on the print window. A 2Dtransmittance profile of the film may be generated by dividing an imageof the film by the background image 200, multiplied by the ratio of theexposure times of those images. In some cases, the image 200 may becaptured every time prior to depositing a new film of the viscousliquid. In some cases, the image 200 may be captured once for every twoor more depositions of the film of the viscous liquid.

Example 2

FIG. 3A shows an example of a 2D image 300 of a film of viscous liquiddeposited on the print window, as captured by the sensor(s). IR lightmay be used as the sensor light(s). FIG. 3B shows an example of a 2Dthickness plot 302 of the film of viscous liquid deposited on the printwindow. The controller may be configured to use a reference (e.g., apreviously obtained plot of film thickness versus sensor light(s)transmittance) to convert at least a portion 310 of the film in the 2Dimage 300 into a greyscale 2D thickness plot 315, as show in the image302. At least the portion 310 of the film in the 2D image 300 may bedivided by the background image 200 prior to converting into thegreyscale 2D thickness plot 315. The image 302 may also exhibitgreyscale values 320 (e.g., greyscale vs. thickness of the film) usedfor the greyscale 2D thickness plot 315. The threshold value of thestandard deviation of the average film thickness may be pre-determinedat 0.01 mm. The measured standard deviation of the 2D thickness plot 315may be 0.0055 mm. As the measured standard deviation of the 2D thicknessplot 315 may be at or below the pre-determined threshold value, the filmshown in the 2D thickness plot 315 may be considered to exhibit auniform film thickness.

Example 3

FIG. 4A shows an example of a 2D image 400 of a film of viscous liquiddeposited on the print window, as captured by the sensor(s). IR lightmay be used as the sensor light(s). FIG. 4B shows an example of a 2Dthickness plot 402 of the film of viscous liquid deposited on the printwindow. The controller may be configured to use a reference (e.g., apreviously obtained plot of film thickness versus sensor light(s)transmittance) to convert at least a portion 410 of the film in the 2Dimage 400 divided by the background image 200 into a greyscale 2Dthickness plot 415, as show in the image 402. At least the portion 410of the film in the 2D image 400 may be divided by the background image200 prior to converting into the greyscale 2D thickness plot 415. Theimage 402 may also exhibit greyscale values 420 (e.g., greyscale vs.thickness of the film) used for the greyscale 2D thickness plot 415. Thethreshold value of the standard deviation of the average film thicknessmay be pre-determined at 0.01 mm. The measured standard deviation of the2D thickness plot 415 may be 0.0185 mm. The measured standard deviationof the 3D thickness plot 415 (e.g., 0.0185 mm) may be higher than thepre-determined threshold value (e.g., 0.01 mm) in part due to one ormore parts 430 of one or more previous layers remaining on the printwindow. As the measured standard deviation of the 2D thickness plot 415may be above the pre-determined threshold value, the film shown in the2D thickness plot 415 may be considered to exhibit a non-uniform filmthickness. As a result, the 3D printing process may be halted.Alternatively or in addition to, a new film of viscous liquid may bedeposited to obtain a uniform film thickness.

Example 4

FIG. 5A shows an example of a 2D image 500, as captured by thesensor(s), of a film of viscous liquid deposited on the print windowprior to printing at least a portion of the 3D object. IR light may beused as the sensor light(s). FIG. 5B shows an example of a 2D image 502,as captured by the sensor(s), of an excess of the film of viscous liquidremaining on the print window subsequent to printing the at least theportion of the 3D object. In the 2D image 502, areas of lowtransmittance 520 of the sensor light(s) may indicate a presence ofexcess viscous liquid on the print window. On the other hand, areas ofhigh transmittance 525 of the sensor light(s) may indicate an absence orlow amount of excess viscous liquid on the print window. Regions of hightransmittance 525 of the sensor light(s) in the 3D image 502 may beusable as a negative image of the previously printed layer of the 3Dobject.

Example 5

FIG. 6 shows an example plot 600 of a thickness of the film of viscousliquid (e.g., y-axis) versus transmittance of the sensor light(s)through the film (e.g., x-axis). Films with different thicknesses (e.g.,verified thicknesses) may be printed on the print window, and thetransmittance of the sensor light(s) through the films may be measuredto obtain the curve 610 of the plot 600. Subsequently, a mathematicalrelationship 620 between the film thickness and the sensor light(s)transmittance as indicated by the curve 610 may be obtained to be usedas a reference to convert any future detection of the sensor light(s)transmittance into a respective film thickness.

Example 6

FIG. 7 shows an example plot 700 of (i) a target width 710 of the filmof viscous liquid, a measured width 720 of the film of the viscousliquid (e.g., as measured by the IR sensor(s)), and a volume of theviscous liquid to be added to or removed from the print window 730during depositing a plurality of films of the viscous liquid versus (ii)a number of printed layers of a 3D object. As shown by the target width710, different widths of the film (e.g., thus different volumes of theviscous liquid in the film) may be required for different layers of the3D object. In an example, according to the target width curve 710, atleast the layers 30-60 of the 3D object may require more viscous liquidin the film (thus a wider film) than at least the layers 1-25 of the 3Dobject. As such, the controller may direct the deposition head todispense additional viscous liquid onto the print window, thereby toprint a wider film of viscous liquid for at least the layers 30-60 ofthe 3D object. The controller may use the sensor(s) to measure the widthof the film 720 for at least the layers 30-60 in real time to adjust thevolume of the viscous liquid to be added to or removed from the printwindow 730, thereby to match the target width 710 of the film of viscousliquid according to in part a computer model of the 3D object. Arelationship between the target width 710 of the film, the measuredwidth 720 of the film (e.g., as measured by the IR sensor(s)), and thevolume of the viscous liquid to be added to or removed from the printwindow may be described in Equation 1:

Vol. of viscous liquid_(added or removed)=κ·(target width−measuredwidth)  (Equation 1)

A constant factor (κ) may be a pre-determined value at a pre-determinedconstant thickness (e.g., 0.01 milliliter (mL) of viscous liquid per 1mm of film width). The factor may be universal for a plurality ofdifferent viscous liquids (e.g., different compositions) or specific foreach type of viscous liquid. In general, an error function may be usedto calculate the deviation of the measured width from the target width,and a control function of that deviation may provide a volume of viscousliquid to be added or removed. The control function may be proportionalto that deviation, as provided in Equation 1. The control function mayalso depend on the integral of the deviation over time, and/or itsderivative with respect to time. The control function may also use fuzzylogic or neural networks or artificial intelligence.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. It is not intendedthat the invention be limited by the specific examples provided withinthe specification. While the invention has been described with referenceto the aforementioned specification, the descriptions and illustrationsof the embodiments herein are not meant to be construed in a limitingsense. Numerous variations, changes, and substitutions will now occur tothose skilled in the art without departing from the invention.Furthermore, it shall be understood that all aspects of the inventionare not limited to the specific depictions, configurations or relativeproportions set forth herein which depend upon a variety of conditionsand variables. It should be understood that various alternatives to theembodiments of the invention described herein may be employed inpracticing the invention. It is therefore contemplated that theinvention shall also cover any such alternatives, modifications,variations or equivalents. It is intended that the following claimsdefine the scope of the invention and that methods and structures withinthe scope of these claims and their equivalents be covered thereby.

1.-44. (canceled)
 45. A system for printing a three-dimensional (3D)object, comprising: a build surface configured to retain a resin duringprinting of said 3D object; a light unit configured to provide light; anoptical diffuser in optical communication with said light unit and saidbuild surface, wherein said optical diffuser is configured to (i)receive said light, (ii) transform at least a portion of said light intodiffused light, and (iii) transmit said diffused light towards saidbuild surface; and a controller operatively coupled to said light unit,wherein said controller is configured to direct said light unit toprovide said light towards said optical diffuser, such that said atleast said portion of said light is transformed by said optical diffuserinto said diffused light and directed towards said build surface duringsaid printing of said 3D object.
 46. The system of claim 45, furthercomprising a sensor in sensing communication with said build surface,wherein said controller is configured to direct said sensor to detect atleast a portion of said diffused light for generating a sensing datathat is indicative of (i) a quality of at least a portion of said resinor (ii) a quality of said build surface.
 47. The system of claim 46,wherein said controller is configured to generate said sensing dataprior to using said at least said portion of said resin for printing atleast a portion of said 3D object.
 48. The system of claim 46, whereinsaid controller is configured to generate said sensing data subsequentto using said resin for printing at least a portion of said 3D object,wherein said at least said portion of said resin comprises any excess ofsaid resin remaining subsequent to said printing.
 49. The system ofclaim 46, wherein said sensing data is indicative of said quality ofsaid build surface.
 50. The system of claim 45, wherein said opticaldiffuser is configured to spread an intensity profile of said at leastsaid portion of said light, to provide said diffused light.
 51. Thesystem of claim 45, wherein said light comprises a wavelength rangingbetween about 700 nanometers and about 1.5 micrometers.
 52. The systemof claim 45, wherein said optical diffuser and said build surface areconfigured to move relative to one another.
 53. The system of claim 45,wherein said optical diffuser and said light unit are configured to moverelative to one another.
 54. The system of claim 45, wherein said lightunit is configured to provide an additional light towards said buildsurface, wherein said additional light is sufficient to cause formationof at least a portion of said resin into at least a portion of said 3Dobject.
 55. A method for printing a three-dimensional (3D) object,comprising: (a) providing: a build surface for retaining a resin; alight unit that provides light; and an optical diffuser in opticalcommunication with said light unit and said build surface; (b) directingsaid light from said light unit to said optical diffuser, which opticaldiffuser transforms at least a portion of said light into diffusedlight; and (c) transmitting said diffused light from said opticaldiffuser towards said build surface during printing of said 3D object.56. The method of claim 55, further comprising using a sensor in sensingcommunication with said build surface to detect at least a portion ofsaid diffused light for generating a sensing data, wherein said sensingdata is indicative of (i) a quality of at least a portion of said resinor (ii) a quality of said build surface.
 57. The method of claim 56,comprising generating said sensing data prior to using said at leastsaid portion of said resin for printing at least a portion of said 3Dobject.
 58. The method of claim 56, comprising generating said sensingdata subsequent to using said resin for printing at least a portion ofsaid 3D object, wherein said at least said portion of said resincomprises any excess of said resin remaining subsequent to saidprinting.
 59. The method of claim 56, wherein said sensing data isindicative of said quality of said build surface.
 60. The method ofclaim 55, wherein said optical diffuser is configured to spread anintensity profile of said at least said portion of said light, toprovide said diffused light.
 61. The method of claim 55, wherein saidlight comprises a wavelength ranging between about 700 nanometers andabout 1.5 micrometers.
 62. The method of claim 55, further comprisingmoving said optical diffuser and said build surface relative to oneanother.
 63. The method of claim 55, further comprising moving saidoptical diffuser and said light unit relative to one another.
 64. Themethod of claim 55, further comprising using said light unit to providean additional light towards said build surface, wherein said additionallight is sufficient to cause formation of at least a portion of saidresin into at least a portion of said 3D object.